EXPERIMENTAL  ENGINEERING 


EXPERIMENTAL  ENGINEERING 


BY 

U.  T.  HOLMES 

Commander,  U.  S.  Navy 


ANNAPOLIS,  MD. 
THE  UNITED  STATES  NAVAL  INSTITUTE 

1911 


COPYRIGHT,  1911,  BY 

W.  B.  WELLS 
Sec'y  and  Treas.  U.  S.  Naval  Institute 


J2or&  (gafttmorc 

BALTIMORE,  MD.,  U.  8.  A. 


EKEATA  SHEET. 
"  EXPERIMENTAL  ENGINEERING."    HOLMES. 

p.  12,  llth  line  from   foot  of  page,  for  "  indeterminute  "  read 
"  indeterminate." 

p.  17,  9th  line,  for  "  ob  "  read  %  db" 

p.  22.  Example  in  middle  of  page,  first  quantity  in  divisor  under 
solution  should  read 


p.  31,  3d  line,  under  "  Special  Slide  Kules,"  strike  out  second 
"for." 

p.  34,  15th  line,  for  "P"  read  "  F." 

p.  35,  5th  line  from  bottom,  for  "grove"  read  "groove." 

p.  57,  Last  line  should  read,  "  Suction  in  chamber  D  will  be  prac- 
tically twice  that  in  chamber  C" 

p.  58,  3d  line,  "  the  specific  volume  will  be  lower  on  passing 
through  B." 

T          T 

p.  105,  Equation  7  should  read,  <f>8  =  a  loge  —  —  +  -=•  . 

p.  157,  Last  line,  for  "adopted"  read  "adapted." 

p.  161,  Fig.  91.  Drop  a  perpendicular  from  the  center  of  the 
shaft  and  indicate  the  horizontal  distance  between  this 
perpendicular  and  one  at  G  as  a. 

p.  171,  4th  line,  formula  should  read: 

MXL      _2_      jr0_ 
~~  EXI  ^  d  ==180* 

10th  line,  for  "moment  of  inertia"  read  "modulus." 
5th  line  from  bottom,  for  "  evaluting  "  read  "  evaluating." 

p.  262,  3d  line  from  bottom,  for  "  gage  "  read  "  gauze." 

p.  263,  21st  line,  for  "  oil  "  read  "  water." 

p.  269,  3d  paragraph  should  read:  The  analysis  of  the  coal, 
referred  to  combustible,  i.  e.,  coal  less  ash  and  water, 
would  be,  in  per  cent:  C,  89.6  (from  83.5  X  100  -=-93.2)  ; 
H,  5.15  ;  0,  3.43  ;  N,  1.29  ;  S,  .536. 


p.  270,  line  9,  should  read:    19.1  x.  896  =  17.1. 

line  19,  should  read  :  ^|  =  .018. 
.oo5 

For  the  sum  of  H20,  "  56,"  read  ".538." 
lines  20  and  21,  19.1  +  .54=  19.64. 
line  21,  17.1  +  .54=  17.64. 
line  22,  17.64  x.  835  =  16.40. 
line  24,  17.64-1  =  16.64. 
p.  271,  line  1,  for  "  17.41  »  read  "17.64." 
line  3,  17.64  x.  246x515  =  2233.5. 
line  9,  for  ".56"  read  ".538." 
line  11,  .538x965.8  =  519.5. 

«.  line  fromfw,t,  . 


p.  272,  line  7,  for  "2206"  read  "2233.5." 
line  9,  for  "  541  "  read  "  519.5." 
line  10,  for  "  341  "  read  "  347.5." 
line  12,  for  "1349"  read  "1346.5." 

p.  273,  5th  line   from   bottom,   insert   words   "  Close  K  "   before 
sentence  beginning  "  Return  leveling  bottle,"  etc. 


PREFACE 

In  attempting  to  revise  the  volume  of  Notes  on  Experimental 
Engineering  compiled  by  the  author  in  1907,  so  much  new  matter 
was  at  hand  and  so  many  changes  were  found  necessary  that  it  was 
deemed  advisable  to  rewrite  the  whole  book.  In  doing  this  con- 
siderable matter  belonging  properly  to  the  subject  of  experimental 
engineering  has  been  brought  in  from  other  text-books. 

The  following  authorities  have  been  consulted :  Carpenter's 
Experimental  Engineering;  Experimental  Engineering,  by  Pullen 
and  Popplewell;  Physical  Laboratory  Notes,  by  Silas  W.  Holman; 
Barton's  Internal  Combustion  Engines ;  Bieg's  Text-Book  on  Naval 
Boilers;  Departmental  Notes;  Smart's  Laboratory  Practice;  Prac- 
tical Cement  Testing,  by  Taylor;  Journal  of  the  American  Society 
of  Mechanical  Engineers ;  Journal  of  the  American  Society  of  Naval 
Engineers;  Power  and  the  Engineer;  various  manufacturers' 
pamphlets.  The  notes  on  the  temperature-entropy  diagram  have, 
for  the  most  part,  been  taken  from  the  article  on  that  subject  by 
Lieutenant-Commander  L.  M.  Nulton,  U.  S.  N.,  published  in  the 
Journal  American  Society  of  Naval  Engineers,  Vol.  VIII.  The 
matter  relating  to  time-firing  devices  has  been  supplied  by  Com- 
mander S.  S.  Eobison,  U.  S.  N.,  of  the  Bureau  of  Steam  En- 
gineering. 

My  thanks  are  due  to  Mr.  F.  H.  Rittenour,  draftsman  in  the  De- 
partment of  Marine  Engineering  and  Naval  Construction,  for  much 
valuable  assistance  in  the  preparation  of  the  illustrations  and  to  Mr. 
J.  M.  Armstrong  for  assistance  in  photographing  apparatus.  Also 
to  the  several  manufacturers  of  engineering  apparatus  for  their 
courtesy  in  supplying  cuts  of  their  laboratory  appliances. 

U.  T.  HOLMES, 

Commander,  U.  S.  N. 
BUREAU  OF  STEAM  ENGINEERING,  NAVY  DEPARTMENT,  May,  1911. 


242289 


CONTENTS 

PAGE 

CHAPTER  I. 

Introduction:  Engineering  calculations — Limits  of  accuracy — 
Measurements — Limits  of  error — Significant  figures — Reports. .  9 

CHAPTER  II. 

Instruments  for  Computing  Experimental  Data:  The  logarithmic 
scale — Different  forms  of  the  logarithmic  scale — The  slide  rule 
— Planimeters  17 

CHAPTER  III. 

Instruments  for  Recording  Experimental  Data:  The  measuring 
machine — Pressure  and  vacuum  gages — Recording  gages — Gage 
testing  apparatus — Thermometers  and  pyrometers — Revolution 
counters — Tachometers — Speed  regulators  40 

CHAPTER  IV. 

Measurement  of  the  Quality  of  Steam:  Definitions  in  thermody- 
namics— Steam  calorimeters  and  their  use — The  temperature- 
entropy  diagram  and  its  uses 85 

CHAPTER  V. 

Measurement  of  the  Rate  of  Flow  of  Water:  Water  meters  of 
various  forms — Weirs  110 

CHAPTER  VI. 

Measurement  of  the  Rate  of  Flow  of  Air  and  Steam:  The  anemom- 
eter— Pitot's  tube  for  low  air  pressures — Steam  flow  meters — 
Air  flow  meters 129 

CHAPTER  VII. 

Measurement  of  Power:  Definitions — The  steam  engine  indicator, 
errors  to  which  it  is  subject  and  methods  of  calibration — Other 
means  of  measuring  power — Dynamometers — The  torsionmeter 
— Calculation  of  shaft  horse  power — Various  forms  of  the  tor- 
sionmeter    144 

CHAPTER  VIII. 

Testing  Materials  of  Construction:  Definitions — Testing  ma- 
chines and  their  operation — Cements — Classification  of  and 
methods  of  testing 187 

CHAPTER  IX. 

Engine  Lubrication:  Systems  of  lubrication — Engine  lubricants- 
Testing  lubricants,  determinations  required  and  apparatus  used 
— Oil  testing  machine — Tests  on  board  ship 212 


* 


"  CONTENTS 


CHAPTER  X. 

The  Selection  and  Testing  of  Fuel:  Testing  coal — Fuel  calorimeters 
and  their  operation — Testing  fuel  oil — Practical  tests  with  the 
Navy  Standard  outfit — Specifications  for  fuel  oils 229 

CHAPTER  XL 

Flue  Gas  Analysis:  The  Orsatt-Muencke  and  Hays  apparatus — 
Automatic  CO2  recorders.  Time  Firing  Devices:  Various  makes 
used  on  naval  vessels .  266 


EXPERIMENTAL  ENGINEERING 


CHAPTER  I. 
INTRODUCTION. 

Experimental  Engineering  is  that  branch  of  the  engineering  pro- 
fession which  treats  of  the  instruments  and  methods  employed  in  the 
collection  of  engineering  data  and  includes  the  testing  of  all 
materials  and  appliances  employed  in  engineering  work.  Mechan- 
isms are  tested  to  determine  the  amount  of  work  done  on  them,  or 
by  them,  and  their  efficiency.  Materials  are  tested  for  the  deter- 
mination of  their  strength,  or  suitability  for  the  purpose  required. 

The  study  of  experimental  engineering  gives  the  student  famil- 
iarity with  the  various  instruments  employed  in  experimental  work, 
together  with  the  methods  of  calibrating  and  of  using  them. 

Materials  under  test  are  seldom  so  homogeneous  that  samples, 
taken  even  from  the  same  piece,  show  exactly  the  same  strength.  In 
efficiency  tests  the  personal  error  of  the  observer  is  usually  such  as 
to  cause  slight  variations  in  the  results  from  different  observations. 
The  results  obtained  in  such  work  can  therefore  have  no  fixed  and 
certain  values,  following  known  laws,  but  will  approximate  more 
or  less  closely  to  the  average  value  which  it  is  desired  to  obtain. 
In  order  to  approximate  as  closely  as  possible  to  the  result,  it  is 
desirable,  where  possible,  to  obtain  the  mean  result  from  a  series 
of  experiments.  Where  it  is  possible  to  secure  only  single  observa- 
tions, it  is  necessary  to  take  more  than  ordinary  precautions  in 
eliminating  all  possible  sources  of  error. 

ENGINEERING  CALCULATIONS. 

Accuracy  with  some  persons  is  instinctive — they  practice  it  in 
every  thought  and  action ;  with  others  it  must  be  cultivated  through 
severe  mental  discipline,  and  they  must  be  continually  on  their 
guard  against  carelessness.  No  one  will  deny  that  accuracy  is  most 


10  EXPERIMENTAL  ENGINEERING 

desirable,  yet  there  is  always  the  chance  of  the  exceedingly  accurate 
person  becoming  absorbed  in  details  without  giving  due  attention 
to  the  main  points.  This  is  especially  true  with  engineering  cal- 
culations, where  it  is  almost  as  bad  to  use  unnecessary  refinements 
as  it  is  to  carelessly  use  a  number  of  crude  approximations.  From 
this  it  should  not  be  inferred  that  precision  may  be  neglected  in 
purely  mathematical  operations.  Forethought  and  discrimination 
are  required  in  determining  the  necessary  degree  of  accuracy.  This 
involves  an  understanding  of  the  relation  which  the  calculation 
bears  to  the  problem  under  consideration,  in  order  that  the  desired 
result  may  be  obtained  without  unnecessary  labor. 

Many  problems  involve  assumptions  or  factors  that  cannot  be  ac- 
curately measured  and  it  would  be  absurd  to  carry  out  the  cal- 
culations to  the  third  or  fourth  decimal  place.  For  instance,  in 
computing  the  load  that  a  certain  member  would  carry,  the  assump- 
tion is  made  that  the  point  of  rupture  of  that  particular  material 
is  50,000  pounds  per  square  inch.  Now,  this  material  may  fail  at 
45,000  pounds  per  square  inch  or  it  may  withstand  55,000  pounds 
per  square  inch;  hence,  the  futility  of  carrying  the  computations 
to  a  high  degree  of  refinement. 

Again,  in  calculating  the  indicated  horse  power  of  a  steam  engine 
from  an  indicator  diagram,  if  a  slide  rule  be  used  the  result  will  be 
about  as  near  the  true  horse  power  as  would  be  the  case  if  the  prob- 
lem were  multiplied  out  in  detail.  The  error  in  finding  the  area 
of  the  indicator  diagram  and  the  fact  that  the  steam  pressure  in 
the  indicator  may  not  exactly  represent  that  in  the  cylinder,  make 
the  result,  at  the  best,  only  approximate. 

On  the  other  hand,  there  are  many  engineering  calculations  which 
require  a  high  degree  of  accuracy.  The  detail  parts  of  a  compli- 
cated piece  of  mechanism,  for  example,  must  be  worked  out  with 
great  precision  in  order  that  the  whole  will  assemble  correctly  when 
finished. 

The  advantage  of  being  able  to  size  up  a  problem  at  a  glance  with 
the  exercise  of  proper  judgment  as  to  the  degree  of  accuracy  re- 
quired, increases  with  experience.  In  the  computing  departments 
of  large  establishments  great  saving  in  time  and  labor  may  be 
effected  by  the  intelligent  use  of  approximations. 


ENGINEERING  CALCULATIONS  11 

Measurements. — Direct  measurements  are  those  that  can  be  read 
directly  such  as  a  measure  of  length,  of  time  or  of  absolute  quantity. 
Indirect  measurements  are  those  which  must  be  calculated  from 
data,  the  different  parts  of  which  may  in  turn  be  measured  directly 
or  indirectly.  Thus  the  horse  power  of  an  engine  is  measured  in- 
directly. The  different  factors  entering  into  it  are  area  of  cylinder 
and  length  of  stroke,  measured  directly,  mean  effective  pressure, 
measured  indirectly,  and  revolutions  per  minute  which  may  be 
measured  directly  by  counting  or  indirectly  from  a  recording  device, 
which  gives  the  revolutions  during  an  interval  of  time  that  must 
be  read  elsewhere. 

Limits  of  Error  in  Observations. — The  purpose  for  which  a  given 
quantity  is  measured  must  determine  the  degree  of  accuracy  which 
we  must  endeavor  to  reach.  This  can  usually  be  stated  definitely 
as  a  numerical  quantity,  or  limits  can  be  assigned;  first  an  upper 
limit  below  which  the  error  must  be  kept  and  a  second  a  lower 
limit  below  which  the  error  will  do  no  injury.  The  extreme  care 
necessary  to  reduce  the  error  below  the  lower  limit  will  be  useless 
and  the  labor  necessary  for  great  refinements  of  accuracy  is  usually 
out  of  proportion  to  the  results  obtained,  so  that  the  lower  limit  is 
often  of  much  importance. 

If  the  measurement  is  direct  it  becomes  only  necessary  to  select 
suitable  apparatus  and  so  operate  it  as  to  produce  a  result  within 
the  assigned  limits  of  accuracy.-  If  it  is  indirect,  we  should  deter- 
mine the  degree  of  accuracy  which  is  necessary  in  each  of  the  various 
component  measurements  from  which  it  is  to  be  computed. 

Deviations  from  the  True  Measurement. — Let  a^  a2,  .  .  .  .,  an  be 
the  various  single  measurements  of  a  quantity  in  a  series,  each  being 
made  with  the  same  care  and  under  the  same  conditions.  These 
values  will  not  usually  be  the  same,  but  will  differ  according  to 
the  quality  of  the  instrument  used,  the  skill  of  the  observer  and 
the  conditions  under  which  he  is  operating.  In  the  case  of  a  series 
of  rough  measurements,  say  of  a  short  distance  to  the  nearest  foot, 
the  various  measurements  may  be  all  alike,  but  even  then  they  might 
differ  by  a  foot  if  the  correct  measurement  were  approximately  half 
a  foot  over  or  under.  If  the  attempt  be  made  to  measure  the  dis- 
tance to  within,  say  one  per  cent,  the  separate  results  will  diverge. 


12  EXPERIMENTAL  ENGINEERING 

Suppose  the  different  measurements  to  have  been  made  with  care, 
and  that  a^  a2,  etc.,  show  sensible  divergence  and  R  is  the  true 
value.  Then  a^  —  R  —  e^  is  the  first  error,  a2  —  R  =  e2  is  the  second, 
etc.  But  R  is  not  known,  else  the  measurements  would  not  be  re- 
quired, hence  the  errors  are  also  not  known.  It  is  therefore  neces- 
sary to  establish  a  rule  for  selecting  a  result  that  will  best  represent 
the  correct  measurement,  and  for  a  series  such  as  that  described, 
experience  has  demonstrated  that  the  arithmetical  mean  best  ful- 
fills this  requirement.  The  most  probable  value  is  therefore  in 
such  a  case 


A  =    i       2  n  ?  where  n  is  the  number  of  single   ob- 

servations. 

If  the  single  observations  are  not  all  equally  reliable,  so  far  as 
known,  then  before  they  are  combined,  some  numerical  measure  of 
their  relative  reliability  or  weight  must  be  taken.  Let  ply  p2,  .  .  .  . 
pn  be  such  numbers,  then  the  most  probable  value  will  be  the 
weighted  mean 

4  -  PI&I+  j?2ga+  ----  +Pnttn 
Pl+P2+  ----  +Pn 

The  variation  of  the  single  observations  will  be  shown  by  their 
deviation  from  the  mean,  viz.:  al  —  A  =  dl,a2  —  A  =  d2,  .  .  .  .  On  —  A 
=  dn.  A  is,  however,  the  mean,  not  the  true  result,  hence  these 
deviations  dly  etc.,  are  not  equal  to  e,  etc.  That  is  the  deviations 
are  not  the  errors  and  must  not  be  confounded  with  them. 

Sources  of  Error  are  of  two  classes,  determinate  and  indeter- 
minute.  Determinate  errors  are  those  inherent  in  the  apparatus, 
such  as  incorrect  scales,  etc.,  and  can  be  corrected  either  absolutely 
or  approximately.  It  is  for  the  elimination  of  errors  of  this  char- 
acter that  apparatus  must  be  carefully  calibrated.  After  all  such 
corrections  that  are  obtainable  have  been  applied,  there  may  still 
remain  a  small  error  in  the  apparatus.  This  is  designated  as  the 
residual  error. 

In  addition  to  the  residual  error  there  are  many  sources  of  error 
affecting  all  observations,  which  cannot  be  discovered  and  allowed 
for.  These  are  all  classed  together  as  indeterminate,  and  are  the 
cause  of  the  deviation  of  the  mean  from  the  true  result.  In  a  large 


ENGINEERING  CALCULATIONS  13 

* 

series  of  observations  made  under  various  conditions  the  effects  of 
the  indeterminate  sources  of  error  are  likely  to  eliminate  each  other 
to  a  large  extent  since  the  errors  of  equal  magnitude  are  about 
equally  likely  to  be  -f-  or  — .  But  in  any  series  of  observations  by 
a  single  method  there  is  a  decided  liability  to  the  preponderance 
of  certain  indeterminate  sources  of  error,  leading  to  a  mean  result 
that  may  differ  considerably  from  that  obtained  by  a  different 
method,  while  in  either  series  the  single  results  may  differ  very 
slightly  from  each  other.  There  is  thus,  in  any  series  of  observa- 
tions, a  liability  to  a  constant  error.  This  can  only  be  eliminated 
by  having  the  observations  made  by  as  many  different  methods,  in- 
struments and  observers  as  is  possible  and  average  the  different  re- 
sults, giving  each  its  proper  weight  as  nearly  as  can  be  determined. 

Mistakes.    Rejection  of  Observations. 

Mistakes  must  not  be  classed  with  errors  of  observation.  They 
arise  from  mental  confusion  which  leads  to  setting  down  a  wrong 
number,  reading  a  scale  division  incorrectly,  selecting  a  wrong 
reference  line,  etc.  Where  one  observation  in  a  series  differs  widely 
from  the  others  it  should  be  checked  over  very  carefully  to  eliminate 
mistakes.  Great  care  and  judgment  must  be  exercised,  after  elimi- 
nating all  mistakes,  in  scrutinizing  such  observations,  in  order  to 
determine  whether  they  should  be  used  with  the  others  or  discarded. 
Some  authors  offer  mathematical  rules  for  guidance  in  such  cases, 
but  the  best  guide  is  the  application  of  scrupulously  honest  un- 
biassed judgment,  in  other  words,  common  sense.  Where  possible 
this  should  be  given  by  some  competent  person  other  than  the 
observer. 

Significant  Figures. — The  term  significant  figures,  in  any  ex- 
pression, refers  to  the  number  of  digits  represented  between  and 
including  the  first  and  the  last,  without  reference  to  the  position  of 
the  decimal  point.  Thus  the  numbers  1234000.,  12.34,  0.0001234, 
5067,  5706,  etc.,  each  have  four  places  of  significant  figures.  In 
computations  involving  the  use  of  observed  data  it  is  important  to 
follow  the  rules  for  the  retention  or  rejection  of  places  of  signifi- 
cant figures,  in  order,  on  the  one  hand,  to  give  the  result  all  the 
accuracy  to  which  it  is  entitled  from  the  data,  and  on  the  other 
hand  to  avoid  encumbering  the  work  with  a  useless  mass  of  figures. 


14  EXPERIMENTAL  ENGINEERING 

Let  M  be  an  original  observed  quantity  and  8  its  average  devia- 
tion. Let  that  place  in  M  which  corresponds  to  the  second  place 
of  significant  figures  in  8  be  called  the  rth  place.  M  is  uncertain 
by  an  amount  8.  Suppose  8  =  0.034,  then  M  is  uncertain  by  34 
units  in  the  rth  place,  by  3  units  in  the  (r—  1)  place  and  is  correct 
in  the  (r— 2)  place.  In  general  the  first  significant  figure  in  the  8 
may  be  anything  from  1  to  9;  hence  M  is  uncertain  by  1  to  9 
units  in  the  (r—l)  place  and  by  10  to  99  units  in  the  r  place.  The 
digit  in  the  (r—l)  place  in  M  is  always  uncertain  and  that  in  the 
r  place  is  so  very  uncertain  as  to  make  its  retention  useless.  Two 
places  of  significant  figures  in  the  8  are  all  that  are  of  service  since 
its  only  use  is  as  an  indication  of  the  correctness  of  M.  These 
considerations  govern  the  retention  of  significant  places  in  the  data. 
Places  may  be  rejected  in  the  result  whose  value  depends  on  the 
doubtful  places  in  the  data. 

Rules  for  Significant  Figures. 

(1)  In  averaging  a  series  of  observations,  results  should  be  carried 
to  two  places  only  beyond  the  point  where  they  become  doubtful. 
Where  the  digit  in  the  first  place  is  large  the  second  digit  is  of 
little  or  no  value. 

(2)  In  a  single  observation,  the  last  place  retained  should  be  the 
second  beyond  which  the  reading  can  be  made  positively,  or  if  the 
digit  in  the  first  place  is  large  the  second  is  unnecessary. 

(3)  In  addition  or  subtraction,  carry  the  sum  or  difference  only 
to  the  second  significant  figure  of  the  least  precise  quantity  in  the 
data. 

(4)  In  multiplication  or  division,  carry  out  the  product  or  quo- 
tient at  any  stage  of  the  work;  only  to  the  number  of  places  corre- 
sponding to  those  retained  in  the  least  precise  factor. 

(5)  In  the  use  of  logarithms,  the  mantissae  should  be  retained  to 
as  many  places  as  there  should  be  significant  figures  retained  ac- 
cording to  rule  4.    The  characteristic  is  not  to  be  considered  as  it 
merely  serves  to  locate  the  decimal  point. 

Take  for  example  the  formula  for  horse  power  in  a  simple  engine, 
viz. : 

I.  H.  P.  =  const,  x  mean  effective  pressure  x  revs,  per  minute. 


ENGINEERING  CALCULATIONS  15 

The  mean  effective  pressure  will  -usually  be  measured  by  an 
averaging  instrument,  giving  the  mean  height  of  card  correct  to 
1/10  inch,  with  a  fairly  close  approximation  to  the  hundredths 
place.  Multiplying  by  the  scale  of  the  spring,  the  mean  effective 
pressure  is  obtained  in  which  the  first  place  is  correct, 'the  second 
is  probably  correct,  the  third  is  doubtful  and  the  fourth  a  very 
doubtful  approximation.  The  revolutions  per  minute  is  obtained 
by  counting  while  observing  the  revolution  of  the  second  hand  of 
a  clock  or  watch.  This  gives  two  places  accurate  after  which  they 
become  doubtful. 

Following  rules  1  and  2,  we  use  three  or  four  places  only  in  ex- 
pressing the  number  of  revolutions  and  the  pressure.  The  constant 
factor  need  only  be  carried  out  to  the  fourth  place  corresponding 
with  the  other  factors.  From  rule  4  it  will  be  seen  that  it  is  use- 
less to  carry  out  the  I.  H.  P.  further  than  to  four  places. 

Another  example  is  that  of  a  ship  making  standardization  trials 
over  the  measured  mile.  Several  observers  agree  on  the  nearest 
second,  but  differ  on  the  tenths.  Averaging  the  observations  the 
rule  provides  for  carrying  out  the  average  to  the  hundredths  place. 
The  number  of  revolutions  on  the  mile  is  given  by  several  counters 
to  the  nearest  whole  number.  The  mean,  applying  the  rule,  is 
carried  to  tenths.  From  these  data  the  speed  per  hour  and  the 
corresponding  revolutions  per  minute  while  on  the  mile  are  cal- 
culated, the  speed  going  to  hundredth  knots  and  the  revolutions 
per  minute  to  tenths.  Having  thus  determined  the  number  of  rev- 
olutions per  minute  for  different  speeds,  we  may  construct  a  curve 
which  will  give  us  the  relation  between  revolutions  per  minute  and 
speeds  per  hour  at  all  practicable  speeds.  To  obtain  the  mean 
speed  during  any  particular  interval  of  time,  it  then  becomes  only 
necessary  to  observe  the  total  number  of  revolutions,  deduce  the 
revolutions  per  minute  and  apply  to  the  curve. 

It  is  obvious  that  to  obtain  the  revolutions  per  minute  with  a 
greater  degree  of  accuracy  than  that  obtained  on  the  measured  mile 
will  be  an  unnecessary  refinement,  and  will  entail  useless  pains  on 
the  part  of  the  observers. 

Computations. — The  labor  involved  in  working  out  the  results  is 
often  greater  than  that  of  taking  the  observations.  In  order  to 


16  EXPERIMENTAL  ENGINEERING 

reduce  this  labor  as  much  as  possible  the  detail  of  the  method  of 
computation  should  be  gone  over  and  simplified  as  much  as  possible, 
rejecting  useless  places  of  figures  and  providing  for  frequent  and 
systematic  checking.  In  the  actual  work  of  computation  the  slide 
rule,  as  hereinafter  described,  will  be  found  most  useful  for  ap- 
proximate results,  while  Fuller's  and  Thacher's  instruments  will  be 
found  accurate  for  computations  involving  four  places  of  signifi- 
cant figures.  The  same  degree  of  accuracy  is  obtained  with  four 
place  logarithms  and  these  will  be  found  sufficiently  accurate  for 
most  work.  The  usual  five  place  tables  may  be  used  for  practically 
any  work. 

It  is  essential  that  all  instruments  used  in  engineering  observa- 
tions should  be  carefully  calibrated. 

Reports. — In  making  reports  on  a  test,  the  following  should  be 
included : 

( 1 )  A  summary  of  the  orders  under  which  the  experiments  or  test 
are  made.    The  orders  themselves  or  copies  should  be  appended  to 
the  report. 

(2)  A  description  of  the  plant  and  apparatus. 

(3)  The  methods  employed  in  carrying  on  the  test. 

(4)  The  observed  and  calculated  data,  tabulated  as  far  as  possible. 
If  blank  forms  are  available  these  should  be  employed  in  making 
out  data  sheets. 

(5)  Conclusions  and  recommendations. 

Any  illustrations  or  drawings  to  accompany  the  report  should  be 
appended.  Reports  should  be  as  concisely  worded  as  possible,  con- 
sistent with  clearness. 


CHAPTER  II. 
INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA. 

The  Logarithmic  Scale. — Take  the  logarithms  of  numbers  from 
1  to  10  and  consider  them  as  representing  dimensions  on  a  linear 
scale  as  shown  in  Fig.  1.  Let  a  and  b  be  two  pointers.  Suppose  a 


i  i  i  i         i       i      i      i     i    i 

O-/oy/  toy 2  /oo3  *y4       /eyS    /ogff  /<y7 /oyd /oy9 /cyM 

FIG.    1. 

to  be  fixed  in  position  and  I  capable  of  movement  to  the  right  or 
left.  Suppose  also  the  scale  to  be  capable  of  movement  along  its 
length. 

If  we  bring  0  on  the  scale  opposite  a,  and  place  b  opposite  log  3, 
the  distance  ab  will  be  equal  to  log  3.  If  then,  without  changing 
the  position  of  I,  we  move  the  scale  to  the  left  the  distance  0&  will 
still  be  log  3.  Suppose  the  scale  to  be  moved  so  as  to  bring  log  2 
opposite  a.  Then  Ob  =  Oa-\-ab  =  log  2+log  3  =  log  6.  It  is  obvious 
that  the  mark  log  6  must  fall  opposite  b.  If  the  scale  be  moved 
further  to  the  left,  bringing  log  3  opposite  a,  Ob  will  equal  log  3 
+  log  3  =  log  9.  The  mark  log  9  will  fall  opposite  b.  If  the  scale 
be  moved  far  enough  to  the  left  b  will  be  off  the  scale.  This  is 
provided  for  by  using  a  second  fixed  pointer  a!9  at  a  distance  from 
a=aa'  =  log  10.  Suppose  log  5  placed  opposite  a,  then  log  10  is  to 
the  left  of  b.  Shift  the  scale,  bringing  log  5  opposite  a'  (Fig.  2). 

a  b  a' 

\  \  \ 

I . I . , . I 

f  I  I  I  I          I         I        \      I      I 

O-Ay/  /og3  /cy3  /oy4      /<yf     fofff  /cy7  /eyff/eyS/by/G 

FIG.  2. 

We  have  aa'  =  log  10  and  &a'  =  log  10  — log  3.  But  log  5  is  opposite 
a'  and  &a'  =  log  5  — 0&. 

.'.  log  10  —  Iog3  =  log    5—  Ob  and 
Ob  =  log    5  +  log  3  —  log  10  =  log  1.5. 


18  EXPERIMENTAL  ENGINEERING 

From  this  it  appears  that  for  problems  in  simple  multiplication, 
dropping  the  subscript  log,  if  we  set  the  scale  to  zero,  i.  e.,  with  a 
falling  at  0,  and  a'  at  10,  bring  the  sliding  pointer  &  opposite  one 
of  the  factors,  then  set  the  scale  to  bring  the  second  factor  opposite 
either  a  or  a',  the  result  of  multiplying  together  the  two  factors  is 
read  at  &. 

For  division,  suppose  that  the  dividend  be  placed  opposite  a'  and 
the  sliding  pointer  moved  opposite  the  divisor  on  the  scale.  Then 
Oa'=log  (dividend)  and  0&=log  (divisor).  ?>a'=log  (dividend) 
—log  (divisor)  =  log  (quotient).  Bringing  0  on  scale,  opposite  & 
the  quotient  is  read  off  opposite  a. 

From  the  foregoing  it  should  be  clear  that  a  logarithmic  scale  is 
one  on  which  the  numbers  set  down  are  the  linear  measurements  of 
the  logarithms  of  the  numbers  so  marked.  It  affords  a  means  of 
mechanically  adding  or  subtracting  the  logarithms  of  numbers  and 
permits  the  number  corresponding  to  the  resulting  logarithm  to  be 
read  off  directly. 

By  making  the  scale  long  enough  and  subdividing  the  divisions, 
it  may  be  made  to  represent  the  logarithms  of  numbers  from  0  to 
1000,  instead  of  0  to  10. 

Sexton's  Omnimetre.  Construction. — Inspection  of  the  instru- 
ment shows  that  it  contains  a  number  of  circles,  each  circle,  or  set 
of  circles,  containing  a  logarithmic  scale  of  some  function.  The 
circles  are  named  and  differently  colored  so  as  to  avoid  danger  of 
confusing  them.  With  their  several  uses,  they  may  be  briefly  de- 
scribed as  follows : 

Outer  Circle.  Logs. — This  circle  gives  a  direct  reading  of  the 
logarithms  of  numbers  shown  on  the  A  circle.  For  any  number 
given  on  A,  we  read  the  decimal  part  of  its  logarithm  opposite  on 
Logs,  as  though  read  from  a  table  of  logarithms.  With  the  instru- 
ment set  to  zero,  i.  e.,  with  LB  opposite  1A,  or  with  the  A  and  B 
scales  coincident,  this  circle  also  gives  the  logarithm  of  any  function 
shown  on  the  various  other  circles.  By  the  term  "  opposite,"  as 
used  herein,  we  mean  on  the  same  radial  line,  utilizing  for  accuracy 
the  straight  line,  or  edge  of  the  runner,  as  a  guide. 

A  Circle. — The  subdivisions  are  to  be  read  as  though  they  were 
figures.  We  may  call  the  starting  point  1,  10,  100,  1000,  etc. 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        19 

The  next  subdivision  to  the  right  will  be  1.005,  10.05,  100.5,  1005, 
etc.;  and  the  second  subdivision  to  the  right,  1.010,  10.10  101.0, 
1010,  etc.,  respectively,  the  value  of  each  subdivision  varying  by  5 
until  we  come  to  2  (or,  20,  200,  etc.) ;  then  we  begin  to  read  by  1 
in  the  third  place  for  each  subdivision,  2.01,  20.1,  201,  etc.,  until 
later,  when  the  value  of  the  subdivision  varies  by  2  in  the  third 
place,  so  that  the  first  subdivision  to  the  left  of  the  starting  point 
is  read  as  9.98,  99.8,  998,  etc. 


FIG.  3. — Sexton's  Omnimetre. 

B  Circle. — The  A  and  B  circles  are  exactly  alike  in  subdivisions 
and  figures.  With  the .  instrument  set  to  zero,  remarks  under  A 
apply  to  B,  as  like  numbers  on  the  two  circles  coincide.  We  may 
regard  scale  B  of  the  instrument  as  the  single  logarithmic  scale 
described  in  the  foregoing  articles.  The  point  1A,  or  zero  point, 
becomes  both  a  and  a'  of  the  description,  while  the  swinging  trans- 
parent pointer  with  hair  line  becomes  the  movable  pointer,  &.  Scales 
A  and  B  constitute  the  scale  and  slide  respectively  of  an  ordinary 
double-scale  slide  rule,  and  may  be  used  for  ordinary  calculations 
according  to  the  explanation  given  on  page  28.  In  the  following 
detailed  explanation  of  the  method  of  using  the  omnimetre,  in 
order  to  avoid  confusing  the  student,  all  operations  are  made  to 


20  EXPERIMENTAL  ENGINEERING 

begin  and  end  with  the  instrument  set  to  zero.  All  the  work  is 
done  with  the  B  scale  only,  the  method  of  operation  being  that 
applicable  to  a  single-scale  slide  rule.  Short-cuts  will  after  a  time 
suggest  themselves  to  the  student,  but  these  are  not  recommended 
until  after  complete  familiarity  with  the  instrument  is  established. 

Squares  or  N2. — The  value  of  the  square  of  any  number  found  on 
Squares  is  opposite  on  B.  If  the  number  is  on  the  inner  Squares 
circle,  its  square  has  1,  3,  5,  etc.,  figures;  if  on  the  outer  circle  of 
Squares,  2,  4,  6,  etc.,,  figures.  If  the  square  root  of  any  number  is 
desired,  first  find  the  number  on  B  then  look  opposite  on  Squares 
for  the  result,  knowing  from  the  foregoing  which  Squares  circle 
will  contain  it,  and  the  number  of  figures  in  the  result. 

Cubes  or  N"3. — The  value  of  the  cube  of  any  number  found  on 
Cubes  is  opposite  on  B.  If  the  number  is  on  the  inner  Cubes  circle, 
its  cube  has  1,  4,  7,  etc.,  figures ;  if  on  the  second  Cubes  circle,  2,  5, 
8,  etc.,  figures;  and  if  on  the  third  or  outer  Cubes  circle,  3,  6,  9,  etc., 
figures.  If  the  cube  root  is  desired,  reverse  the  operation.  Take  the 
number  from  B  and,  having  in  mind  the  foregoing  explanation,  the 
proper  Cubes  circle  in  which  to  find  the  result  and  the  number  of 
figures  it  should  contain,  will  be  determined. 

Fifth  Powers  or  N5. — The  value  of  the  fifth  power  of  any  num- 
ber found  on  an  N5  circle  is  opposite  on  B.  For  numbers  on  the 
inner  circle  of  N5,  the  fifth  power  has  1,  6,  11,  etc.,  figures;  on  the 
second  circle,  2,  7,  12,  etc.,  figures;  on  the  third  circle,  3,  8,  13,  etc., 
figures ;  on  the  fourth  circle,  4,  9,  14,  etc.,  figures ;  and  on  the  fifth 
or  outer  circle,  5,  10,  15,  etc.,  figures.  If  the  fifth  root  is  desired, 
the  reverse  operation  is  followed  as  explained  before. 

Trigonometric  Functions. — The  numerical  (natural)  value  of  the 
secant,  sine,  tangent,  or  versed  sine  of  any  angle  is  found  on  B 
opposite  the  given  angle  on  the  circle  of  appropriate  name.  Setting 
the  instrument  to  zero,  the  corresponding  logarithmic  function  is 
read  on  the  outer  circle.  The  following  explanation  gives  the 
method  of  finding  the  decimal  point  in  various  cases. 

Secants. — There  is  no  difficulty  in  locating  the  decimal  point,  as 
the  secant  of  any  angle  is  greater  than  unity,  and  within  the  limits 
of  the  instrument  lies  between  1  and  10. 

Sines. — If  the  angle  is  between  0°  35'  and  5°  45',  use  the  inner 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        21 

Sin.  circle  and  read  0.01  to  0.10  on  B.  Between  5°  45'  and  86°, 
use  the  outer  circle  and  read  0.10  to  1.00. 

Tangents.—  If  the  angle  is  between  0°  35'  and  5°  43',  use  the 
inner  Tang,  circle  and  read  0.01  to  0.10  on  B.  If  between  5°  43' 
and  45°,  use  the  middle  circle  and  read  0.10  to  1.00  on  B.  If 
between  45°  and  84°  15',  use  the  outer  circle  and  read  from  1.00 
to  10.00  on  B. 

Versed  Sines.  —  If  the  angle  is  between  2°  35'  and  8°  05',  use 
the  inner  circle  and  read  0.001  to  0.01  on  B.  If  between  8°  .05'  and 
25°  50',  use  the  middle  circle  and  read  0.01  to  0.1.  If  between 
25°  50'  and  90°,  use  the  outer  circle  and  read  0.1  to  1.0. 

Multiplication  and  Division.  —  In  the  use  of  the  omnimetre  as  a 
calculating  instrument  for  formulae  involving  multiplication  and 
division  of  any  of  the  functions  given  on  the  various  slide  circles, 
a  few  experiments  wrill  emphasize  the  following  useful  points  : 

(a)  The  formula  should  always  be  expressed  in  the  form-  of  a 
fraction  in  which  : 

/TX      No.  of  factors  in  numerator      11-11  T      •     .1 

(b)  T?  -  TT~~     —•  —  j  --  —     "   should  always  be  in  the  ratio 
No.  oi  factors  in  denominator 

of  *±1  . 

X 

Example  1  :     Eequired  the  value  of  ax^xc  .     This  should  be 

a  x  b  x  c 
written  —  -=  —  -  —  ,  unity  being  in  all  cases  substituted  for  any  of 

the  missing  factors. 
Example  2: 

of  expression  is 


Example  2:  Eequired  the  value  of   -  —  ^  -  .    The  proper  form 

u  x  a  x  c 


bxdxc 
Example  3 :    Eequired  the  value  of  x  from  the  equation : 

x_  a*xsmbxcxdsxe 

t&nfxg2 
a*  X  sin  b 


Write  the  equation  as  *= 

tan/x#2Xlxl 

a,  b,  c,  etc.,  may,  of  course,  be  given  any  value  that  can  be  found 
on  any  circle  of  the  slide.) 


22  EXPERIMENTAL  ENGINEERING 

In  problems  involving  the  use  of  the  cosine,  cosecant,  or  cotan- 
gent, these  functions  should  be  written  in  the  form : 

,  respectively. 

secant     sine     tangent ' 

(c)  Having  the  problem  expressed  in  proper  form,  as  above,  the 
first  move  is  to  set  the  instrument  to  zero,  i.  e.,  IA  on  15,  so  that 
like  numbers  on  scale  and  slide  coincide. 

(d)  For  all  factors  in  the  numerator  move  the  runner  over  the 
slide,  keeping  the  scale  and  slide  stationary. 

(e)  For  all  factors  in  the  denominator  move  the  slide  under  the 
runner  until  the  required  number  on  the  slide  comes  under  the 
radial  line  of  the  runner,  keeping  the  scale  and  runner  stationary. 

(f )  Alternate  the  movements  of  runner  and  slide. 

(g)  The  last  move  is  to  set  the  slide  to  zero  (IA  on  15),  keeping 
runner  and  scale  stationary,  and  along  the  runner  in  the  proper 
circle  will  be  found  the  required  answer. 

Example :    Required  the  value  of  x  from  the  equation : 

0.296  X  73  X  0.00115  x  97.6  X  33.2 
.012x671.5 

Solution: 

m      _  0.296  X  73  X  0.00115  X  97.6  x  33.2 
0.12X671.5X1X1 

(2)  Set  the  instrument  to  zero. 

(3)  Move  runner  to  296  on  slide  B. 

(4)  Bring  12  on  slide  under  runner. 

(5)  Move  runner  to  73  on  slide  B. 

(6)  Bring  6715  on  slide  under  runner. 

(7)  Move  runner  to  115  on  slide  B. 

(8)  Bring  unity  on  slide  under  runner. 

(9)  Move  runner  to  976  on  slide  B. 

(10)  Bring  unity  on  slide  under  runner. 

(11)  Move  runner  to  332  on  slide  B. 

(12)  Set  the  instrument  to  zero. 

(13)  Eead  numerical  value  of  x  on  B  (or  A),  as  indicated  by 
runner. 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        23 

(14)   Find  position  of  decimal  point  by  rough  calculation. 

Var.  1:  If,  instead  of  x,  we  have  x2,  x5,  or  x5,  then,  after  (12), 
read  value  of  x  from  Squares,  Cubes  or  N5,  as  the  case  may  be. 

Var.  2:  If,  instead  of  x,  we  have  Vz,  8Va?,  5Vx,  then,  after 
(12),  select  from  B  the  number  indicated  by  the  runner,  and  with 
this  number  enter  Squares,  Cubes,  or  N5,  and  the  value  of  x  will  he 
found  opposite  on  B. 

Var.  3 :  If,  instead  of  x,  we  have  sec  0,  sin  6,  tan  0,  or  vers 
sin  B,  then,  after  (12),  the  value  of  0  as  an  angle  is  read  from  the 
circle  Sec.,  Sin.,  Tang.,  or  V.  S.,  as  the  case  may  be. 

As  an  example  involving  functions  of  the  omnimetre,  suppose 
we  assume 

_  sin  14°  x  tan  4o°  x  sec  (39°  20')  x  vers  sin  (27°  45')  x  (4.7)3 

(36.7572~X  (1.965)3 

sin  14°  x  tan  43°  X  sec  (39°  20')  x  vers  sin  (27°  45')  x  (4.7)3 
(36.75)2  X(l.»65px  IX  1 

(2)  Set  the  instrument  to  zero. 

(3)  Move  runner  to  14°  on  slide  Sin. 

(4)  Bring  3675  on  slide  N2  to  runner. 

(5)  Move  runner  to  43°  on  slide  Tang. 

(6)  Bring  1965  on  slide  Ns  to  runner. 

(7)  Move  runner  to  39°  20'  on  slide  Sec. 

(8)  Bring  unity  on  slide  B  to  runner. 

(9)  Move  runner  to  27°  45'  on  slide  V.  S. 

(10)  Bring  unity  on  slide  B  to  runner. 

(11)  Move  runner  to  47  on  slide  N8. 

(12)  Set  instrument  to  zero. 

(13)  Eead  value  of  x  on  B  as  indicated  by  runner. 

(14)  Make  rough  calculation  for  decimal  point. 

Special  Cases. — The  method  of  using  the  instrument  in  the  solu- 
tion of  a  few  well-known  formulae  may  be  illustrated  as  follows : 

Case  1 :  Should  a  formula  contain  a  simple  factor  multiplied  by 
a  radical,  it  is  much  easier  of  solution  to  introduce  the  simple  factor 
under  the  radical,  and  extract  the  root  as  a  last  operation. 

Example:  Find  the  diameter  of  a  shaft  to  transmit  4850  I.  H.  P. 
at  165  revolutions. 


24  EXPERIMENTAL  ENGINEERING 

The  formula  is  : 


where  K  =  constant  =  4.  3. 
Solution: 


(1)   d=4.3^^=    7(4^X4850 
V   1  V 


165  165 

(2)  Set  the  instrument  to  zero. 

(3)  Move  runner  to  43  on  slide  N3. 

(4)  Bring  165  on  slide  B  to  runner. 

(5)  Move  runner  to  485  on  slide  B. 

(6)  Set  instrument  to  zero. 

(7)  Eead  value  of  d  on  Ns  as  indicated  by  runner. 

(8)  Make  rough  calculation  for  decimal  point. 

Example  2:  Find  the  thickness  of  a  flat  cylinder  cover  for  a 
pressure  of  165  pounds.  Tensile  strength  allowed  10000.  Diame- 
ter of  cylinder  11.5  inches. 

The  formula  is  : 


Solution: 


-V 


(5.75)2X£X165 


3X10000  3X10000 

(2)  Set  the  instrument  to  zero. 

(3)  Move  runner  to  575  on  slide  N2. 

(4)  Bring  3  on  slide  B  to  runner. 

(5)  Move  runner  to  2  on  slide  B. 

(6)  Bring  1  on  slide  B  to  runner. 

(7)  Move  runner  to  165  on  slide  B. 

(8)  Set  instrument  to  zero. 

(9)  Read  value  of  t  from  slide  N2. 

(10)  Make  rough  calculation  for  decimal  point. 

Case  2:     To  find  the  square  root  of  the  sum  of  two  squares 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        25 

Find  the  angle  (6)  whose  tangent  is -—-and  divide  a  by  the  sine 
of  this  angle. 

The  reason  for  this  may  be  seen  by  referring  to  Fig.  4,  in  which 


and 


t  an  0=4 

o 


sin  6  =  — p=  ==  ; 

vV+62 


sin  B  '  pIG.  4. 

Example :    Find  the  equivalent  twisting  moment  of  a  solid  shaft 
from  the  formula  Te  =  M+  ^/M2  +  T2. 
Solution: 
( 1 )   Consider  the  part  under  the  radical  and  write 


and 


_ 

~ 


sin  B       sin  B  ' 

(2)  Set  the  instrument  to  zero. 

(3)  Move  runner  to  a  on  slide  B. 

(4)  Bring  b  on  slide  B  to  runner. 

(5)  Move  runner  to  unity  on  slide  B. 

(6)  Set  instrument  to  zero. 

(7)  Note  value  of  B  on  slide  Tang. 

(8)  Move  runner  to  a  on  slide  B. 

(  9  )  Bring  6  on  slide  Sin.  to  runner. 

(10)  Move  runner  to  unity  on  slide  B. 

(11)  Set  instrument  to  zero  and  read  value  of  x  on  slide  B,  plac- 
ing decimal  point. 

(12)  The  value  of  Te  =  x  +  M. 

Case  3:    To  find  the  square  root  of  the  difference  of  two  squares 


26 


EXPERIMENTAL  ENGINEERING 


Find  the  angle  (0),  whose  sine  is — ,  and  divide  a  by  the  secant 

of  this  angle.    The  reason  for  this  may  be  seen  by  referring  to  Fig. 
5,  in  which 


sin  0,  - 


b    and 


sec  9— 


sec0' 


Example:    Find  the  load  that  a  screw  thread  will  safely  sustain, 
having  given  the  formula : 

W=Kxnx~-X(di2-d22). 
Solution:     (I)   Consider  the  part  in  parenthesis  and  write 


sin  0=  -~  = 
a 


,  and  x  = 


sec  0 


oxl 

sec0* 


(2)  Set  the  instrument  to  zero. 

(3)  Move  runner  to  b  on  slide  B. 

(4)  Bring  a  on  slide  B  to  runner. 

(5)  Move  runner  to  unity  on  slide  B. 

(6)  Set  instrument  to  zero. 

(7)  Note  value  of  6  on  slide  Sin. 

(8)  Move  runner  to  a  on  slide  B. 

(9)  Bring  6  on  slide  Sec.  to  runner. 

(10)  Move  runner  to  unity  on  slide  B. 

(11)  Set  instrument  to  zero  and  read  value  of  x2  from  N*9  plac- 
ing decimal  point. 

(12)  We  now  have  W=KxnX  ~  Xx2= 

4 

is  in  proper  form  for  solution  in  the  usual  manner. 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA 


Fuller's  Calculating  Instrument. — This  in- 
strument, shown  in  Fig.  6,  is  a  single  logarithmic 
scale  about  83  feet  in  length,  wound  spirally  on 
a  cylinder  B.  This  cylinder  is  capable  of  a 
movement  of  rotation,  as  well  as  a  vertical  move- 
ment on  the  cylinder  A.  The  fixed  pointers  a 
and  a'  are  carried  on  cylinder  A,  while  the  mov- 
able pointer  b  is  attached  to  the  handle  H  and 
is  capable  of  a  vertical,  as  well  as  a  rotary  move- 
ment. The  instrument  is  thus  seen  to  be  the 
same  in  principle  as  that  described  above.  The 
length  of  scale  permits  calculations  correspond- 
ing in  accuracy  to  those  obtained  with  the  use  of 
four  place  logarithms. 

Sperry's  Pocket  Calculator. — This  is  another 
example  of  the  single  logarithmic  scale  and  is 
made  up  in  the  form  of  a  watch  as  shown  in  Fig. 
7.  There  are  two  dials  on  the  two  opposite  faces, 
as  shown.  The  L  dial  contains  a  single  logarith- 
mic scale  about  12J  inches  long,  arranged  in 
three  spirals,  beginning  and  ending  on  the  same 
radial  line.  A  mark  on  the  glass  face  constitutes 
the  fixed  pointer,  which  corresponds  to  both  a 
and  a'  of  page  17,  since  0  and  10  are  both  found 
on  the  same  radial  line.  The  dial  carrying  the 
scale  is  movable,  as  well  as  a  hand  corresponding 
to  the  movable  pointer  &. 


FIG.  6. 


L  DIAL. 


S  DIAL. 


FIG.  7. 


EXPERIMENTAL  ENGINEERING 


The  S  dial  bears  a  scale  of  equal  parts,  a  circular 
logarithmic  scale,  and  a  scale  of  square  roots. 

This  is  a  very  convenient  instrument  for  rough 
calculations,  but  the  scale  is  not  long  enough  for 
calculations  requiring  accuracy. 

The  Slide  Rule. — This  instrument,  the  most 
common  adaptation  of  the  logarithmic  scale  is 
illustrated  in  Fig.  8.  There  are  two  scales,  simi- 
larly constructed,  arranged  to  slide  one  on  the 
other.  There  is  also  a  sliding  pointer,  or  "  runner," 
used  in  reading  off  the  results.  For  convenience 
in  the  following  description  the  two  scales  will  be 
designated  as  the  "scale"  and  the  "slide,"  re- 
spectively. 

Operation. — For  any  position  of  the  slide  rela- 
tive to  the  scale  it  is  obvious  that  every  number  on 
the  slide  will  bear  the  same  ratio  to  the  number 
opposite  it  on  the  scale.  For  example,  bring  7  on 
the  slide  opposite  10  on  the  scale.  The  ratio  7: 
10  =  I:-1/,  will  be  found  along  the  whole  length 
of  the  rule.  The  number  on  scale  opposite  any 
other  number  on  slide  will  be  the  product  of  that 
number  multiplied  by  10,  divided  by  7.  For  ex- 
ample, opposite  2.1  on  slide  we  read  3.  We  have 

then  divided  10  by  7  and  multiplied  by  2.1.  WX2'1 

=  3.  Obviously  unity  may  be  substituted  for  any 
one  of  these  factors.  Therefore  to  multiply  any 
two  numbers  together,  bring  unity  on  slide  opposite 
one  of  the  numbers  on  scale*  then  opposite  the 
other  number  on  slide  read  the  product  on  scale. 
In  multiplying  and  dividing  a  number  of  factors, 
by  using  the  runner,  the  necessity  for  reading  the 
scale  each  time  the  slide  is  moved  may  be  avoided. 
For  example:  Multiply  6x7x3  and  divide  by 

8x2. 

6x7x3 


X2 


PIG.  8. 


(28) 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        29 

The  factors  in  the  numerator  show  the  successive  positions  which 
the  runner  must  take  and  those  in  the  denominator  the  positions  of 
the  slide.  (1)  Start  with  runner  opposite  6  on  scale.  (2)  Bring 
8  on  slide  to  runner.  (3)  Move  runner  to  7  on  slide.  (4)  Bring  2 
on  slide  to  runner.  (5)  Move  runner  to  3  on  slide.  The  result  is 
then  read  directly  on  the  scale  opposite  runner. 

The  method  of  operation  is  thus  seen  to  be  one  of  alternately 
dividing  and  multiplying.  Until  complete  familiarity  with  the 
operation  of  the  instrument  is  established,  the  factors  should  be  so 
arranged,  substituting  unity  for  any  of  the  factors  that  may  be 
missing. 


FIG.  9. 

The  numbers  on  the  slide  rule  are  to  be  considered  significant 
figures,  and  to  be  used  without  regard  to  the  decimal  point.  Thus 
the  number  on  the  rule  for  8  is  to  be  used  as  8  or  80  or  800,  etc., 
as  may  be  desired,  even  in  the  same  problem.  The  position  of  the 
decimal  point  in  the  result  is  readily  determined  by  a  rough  compu- 
tation. In  case  the  slide  projects  so  much  beyond  the  scale,  that  the 
runner  cannot  be  set  at  the  required  figure  on  the  slide,  bring  the 
runner  to  1  on  the  slide,  then  move  the  slide  its  full  length,  until  the 
other  1  comes  under  the  runner.  Then  proceed  as  before,  moving 
runner  to  number  on  slide  and  reading  results  on  scale. 

The  ordinary  straight  slide  rule  as  shown  in  Fig.  8  is  in  two 
parts,  one  above  and  one  below,  either  of  which  can  be  used.  The 
upper,  being  to  half  the  scale  of  the  lower,  is  not  so  accurate,  but  is 
more  convenient  for  rough  computations.  On  the  back  of  the  slide 
are  two  other  scales,  usually  of  logarithmic  trigonometric  functions. 
The  slide  is  reversed  when  it  is  desired  to  use  them. 
3 


30 


EXPERIMENTAL  ENGINEERING 


Thacher's  Calculating  Instrument. — This  instrument,  shown  in 
Fig.  9,  is  adapted  to  calculations  requiring  a  considerable  degree  of 
accuracy.  Logarithmic  scales,  about  50  feet  long  are  cut  up  into 
sections  of  about  18  inches  and  the  various  sections  for  the  slide 
are  placed  on  a  cylinder  about  4  inches  in  diameter.  For  the  scale, 
the  sections  are  placed  on  a  surrounding  cage.  The  marking  is 
finely  subdivided  and  a  glass  is  provided  for  reading  it.  The  method 
of  operation  is  identical  with  that  of  the  slide  rule. 

The  Duplex  Slide  Rule. — This  instrument,  shown  in  Fig.  10,  is 
graduated  on  both  faces,  thus  practically  giving  two  rules  in  one. 


FRONT  VIEW   OF   DUPLEX   SLIDE   RULE. 


BACK   VIEW   OF   THE   RULE,    SHOWING    THE   INVERTED   SCALES. 
FIG.    10. 

The  front  face,  shown  in  the  upper  view,  is  an  ordinary  slide  rule 
in  which  both  the  scale  and  the  slide  are  graduated  from  left  to 
right.  On  the  rear  face,  shown  in  the  lower  view,  the  graduations  on 
the  scale  are  the  same  as  on  the  front  face  but  the  slide  is  graduated 
from  right  to  left.  The  scales  on  both  sides  have  their  indexes  in 
alignment  so  that  the  runner,  which  encircles  the  whole  instrument, 
permits  coinciding  points  on  all  scales  of  either  face  to  be  read  off 
at  once. 

The  advantage  of  the  duplex  slide  rule  lies  in  the  reduction  of  the 
number  of  settings  required  in  performing  calculations  involving 
several  factors,  thus  saving  time  and  giving  increased  accuracy. 
This  follows  because  when  setting  to  quantities  on  the  inverted 
slide,  the  reciprocals  of  these  quantities  are  given  opposite  on  the 
regular  slide,  and  vice  versa,  so  that  the  operations  of  multiplica- 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        31 

tion  and  division  are  reversed.  What  is  a  dividing  operation  with 
the  regular  slide  becomes  a  multiplication  process  with  the  inverted 
one.  Thus  in  compound  multiplication  the  solution  may  be  effected 
by  a  combination  of  multiplication  and  division  operations,  by  using 
the  regular  inverted  slides,  with  a  consequent  reduction  in  the 
number  of  settings.  A  similar  method  may  be  followed  with  a 
division  operation  when  there  are  a  number  of  factors  in  the  de- 
nominator, as  the  multiplication  by  a  reciprocal  performs  a  division 
process. 

Suppose  it  be  required  to  solve  a  problem  in  the  form  a  X  b  X  c. 
With  this  form  of  instrument,  using  the  designations  for  the  scales 
as  shown  on  Fig.  10,  set  &  on  C,  to  a  on  D  and  under  c  on  C  read 
the  result. 

If  it  be  required  to  solve  ,  ..     ,  set  &  on  C  to  a  on  D  and  under  c 

u  x  c 

on  C,  read  the  result. 

These  operations,  which  are  performed  at  a  single  setting  of  the 
duplex  slide  rule,  require  two  settings  with  the  ordinary  slide  rule 
and  three  with  the  single  logarithmic  scale. 

Complete  familiarity  with  this  instrument  can  only  be  acquired 
from  practice,  when  it  will  be  found  a  great  time  saver. 

Special  Slide  Rules. — Many  calculating  instruments  for  special 
purposes,  have  been  made,  involving  the  principles  of  the  logarithmic 
scale  and  slide  rule.  Two  of  these  for  for  calculating  horse  power 
will  be  found  in  another  chapter. 

PLANIMETERS. 

The  Amsler  Polar  Planimeter. — This  is  the  original  planimeter 
or  mechanical  integrator  of  Dr.  Amsler  and  is  shown  in  Fig.  11. 
A  radius  rod  OP  contains  a  needle  point  P  which  acts  as  the  center 
around  which  it  turns.  This  point  is  loaded  with  a  weight  to  main- 
tain it  in  position  while  in  use.  It  is  preferable  to  use  the  instru- 
ment on  a  drawing  board  which  has  been  previously  covered  with  a 
smooth,  hard  paper.  Eough  paper  should  not  be  used.  The  other 
end  of  the  radius  rod  is  pivoted  to  a  saddle  which  slides  along  the 
square  rod  shown  in  a  horizontal  position,  and  which  carries  the 
tracing  point  F.  This  saddle  also  carries  the  recording  wheel  D 


32  EXPERIMENTAL  ENGINEERING 

with  its  spindle  and  worm,  together  with  the  recording  disc  G  and 
a  worm  wheel  for  actuating  it.  The  saddle,  which  is  secured  to  the 
tracing  rod  by  means  of  a  clamping  screw  S,  contains  the  fine  ad- 
justment screw,  shown  at  the  left,  by  which  it  can  be  accurately 
placed  in  position  on  the  tracing  bar.  The  several  marks  on  the 
tracing  bar  indicate  the  units  in  which  the  area  to  be  traced  may  be 
recorded  by  the  instrument,  with  the  multiplier  that  is  to  be  used 
in  each  case. 

To  use  the  instrument  the  saddle  is  placed  on  the  tracing  bar 
and  carefully  brought  to  the  mark  corresponding  to  the  unit  in 
which  it  is  desired  to  find  the  area.  The  fixed  center  P  is  then 


FIG.  11. 


placed  somewhere  outside  the  area  that  is  to  be  traced.  The  tracing 
point  F  is  then  brought  to  a  position  on  the  outline  of  the  figure 
and  a  point  pricked  there.  The  graduated  disc  Df  wheel  G,  and 
vernier  E  are  read  and  recorded.  Trace  the  outline  of  the  area,  fol- 
lowing in  the  direction  of  the  hands  of  a  watch,  returning  to  the 
point  previously  marked.  Again  take  the  reading  and  substract 
from  it  the  previous  reading.  Multiply  this  remainder  by  the  con- 
stant indicated  on  the  tracing  bar  and  the  result  will  give  the  area 
in  terms  of  the  required  unit. 

We  may  consider  a  circle  of  such  diameter  that  with  the  fixed 
point  P  as  its  center  and  the  tracing  point  following  its  circumfer- 
ence the  tracing  wheel  will  constantly  move  in  a  direction  along  its 
own  axis,  producing  no  rotation  of  the  wheel.  This  will  occur  when 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        33 

the  angle  PDF  is  a  right  angle.  Obviously  no  change  in  reading 
of  the  wheel  can  result  and  this  circle  is  called  the  zero  circle.  In 
case  an  area  to  be  measured  is  so  large  that  it  cannot  be  traced  with 
the  fixed  point  P  placed  outside,  it  may  be  placed  inside  the  figure, 
but  in  this  case  a  correction  must  be  added  equal  to  the  area  of  the 
zero  circle.  This  correction  is  marked  on  the  tracing  bar  for  each 
of  the  several  positions  of  the  saddle.  m 


FIG.  12. 

Theory  of  the  Instrument. — In  the  diagrammatic  Fig.  12,  OT 
is  the  zero  circle  with  radius  F'P  such  that  a  perpendicular  from 
P  on  F'D'  falls  at  Df,  passing  through  the  plane  of  the  wheel.  AFB 
is  a  line  lying  outside  of  the  zero  circle  with  an  area  lying  between 
it  and  the  zero  circle  that  is  to  be  measured.  Suppose  the  pointer 
F  is  made  to  trace  an  elementary  portion  of  this  area  included  in 
the  angle  dB.  The  movement  begins  at  F,  extends  radially  to  the 


34  EXPERIMENTAL  ENGINEERING 

zero  circle,  then  along  the  zero  circle  through  the  angle  d6,  then 
radially  through  the  distance  F'F  to  AFB,  then  along  AFB  through 
angle  d6,  back  again  to  F.  It  is  evident  that  the  first  and  third 
movements  are  equal  and  opposite  in  direction,  each  causing  a  rota- 
tion of  the  wheel,  but  with  the  two  movements  serving  to  nullify 
each  other.  The  second  movement  along  the  zero  circle  causes  no 
rotation  of  the  wheel.  There  remains  the  fourth  movement  along 
AFB  which  will  be  registered  on  the  wheel  when  the  pointer  re- 
turns to  F. 

Consider  the  pointer  in  the  position  F,  with  the  wheel  at  D  and 
the  pivot  at  C.  While  F  is  moving  through  the  angle  dO  its  in- 
stantaneous center  is  P.  C  also  swings  about  P  which  is  therefore 
the  instantaneous  center  for  the  whole  rod  FD.  The  movements 
of  F  and  D  are  then  in  the  proportion  PF  :  'PD.  The  linear  move- 
ment of  P  is  PFdO  and  of  D  is  PDdB.  Drop  a  perpendicular  from 
P  on  FD  extended.  The  linear  movement  of  D,  which  is  propor- 
tional to  PD,  can  be  resolved  into  components,  one  parallel  to  FD 
which  is  proportional  to  PM  and  causes  no  movement  of  the  wheel, 
the  other  perpendicular  to  FD,  which  is  proportional  to  DM  and 
causes  a  linear  movement  of  the  circumference  of  the  wheel  that 
we  will  call  dR. 

Let  m  =  length  of  arm  PC. 
1  =  length  of  arm  OF. 
n—  distance  from  pivot  to  wheel. 

dR  =  DMdO=(mco$p-n)d0.  (1) 

The  area  of  the  element  traced, 

dA=%(r>-r'2)d0.  (2) 

In  the  triangle  PFC  we  have 

r2  =  m2  +  l2  +  2mlcosfi.  (3) 

In  the  right  triangle  PFfD'  we  have 

r'*=<PD'2+(l  +  n)2  =  m2-n2+(l  +  n)2  =  m2  +  l2  +  2nl       (4) 
From  (3)  and  (4), 


and 

dA  =  l(mcosj3-n)de.  (5) 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        35 
From  (1)  and  (5) 


(6) 
Integrating  between  the  limits  0  and  R 


This  shows  that  the  area  is  equal  to  the  length  of  arm  from  pivot 
to  tracing  point,  multiplied  by  the  space  registered  on  the  circum- 
ference of  the  record  wheel,  and  is  independent  of  the  other  dimen- 
sions of  the  instrument. 

This  is  also  true  for  areas  not  adjacent  to  the  zero  circle,  or  for 
areas  partly  inside  and  out,  as  can  be  proved  by  subtracting  the  areas 
between  the  zero  circle  and  the  given  area.  The  demonstration  is 
general. 

The  instrument  is  usually  constructed  so  that  the  arm  /  is  adjust- 
able in  length,  permitting  its  use  for  any  scale  or  for  various  units. 
In  the  No.  3  Amsler  planimeter,  shown  in  Fig.  11,  two  points  are 
shown  on  the  back,  one  on  the  tracing  bar  and  the  other  on  the 
saddle.  The  length  between  them  equals  I  and  by  adjusting  the 
saddle  so  that  this  length  is  that  of  an  indicator  card,  the  reading 
of  the  wheel  will  give  the  mean  height  of  the  card  in  fortieths  of  an 
inch. 

Coffin's  Averaging  Instrument.  —  This  instrument  shown  in  Fig. 
13  may  be  considered  as  a  special  form  of  Amsler's  planimeter  in 
which  the  radius  rod  m  is  of  infinite  length,  the  point  C,  Fig.  12, 
being  constrained  to  move  in  straight  lines.  It  is  commonly  em- 
ployed for  measuring  mean  effective  pressures  from  indicator  cards. 
It  consists  essentially  of  a  rod  having  on  one  end  a  tracing  point  0, 
which  is  moved  over  the  outline  of  the  diagram.  The  other  end  of 
the  rod  contains  a  pin,  which  slides  in  the  groove  in  the  plate  I, 
on  the  left  of  the  figure,  the  pin  being  maintained  in  contact  with 
the  grove  by  the  weight  Q.  The  rod  also  contains  the  bearings  for 
the  spindle  of  the  graduated  wheel,  near  the  lower  edge  of  the  figure. 
The  rod  is  thus  supported  on  three  points,  namely,  the  tracing  point 
Q,  the  pin  Q,  and  the  flange  of  the  graduated  wheel.  Attached  to 
the  board  are  a  pair  of  clips  C  and  K,  of  which  the  latter  is  capable 


36 


EXPERIMENTAL  ENGINEERING 


of  being  moved  parallel  to  itself  by  means  of  the  slide  at  its  lower 
extremity.  One  of  the  horns  of  the  rod  which  supports  the  gradu- 
ated wheel  is  divided  so  as  to  form  a  vernier  for  the  more  accurate 
reading  of  the  graduations. 

To  obtain  the  mean  height  of  an  area  (in  the  figure  an  indicator 
diagram)  slide  the  paper  containing  the  area  under  the  two  clips 


FIG.  13. 


C  and  Kt  and  arrange  it  so  that  a  horizontal  line  of  the  diagram  is 
parallel  to  the  horizontal  edge  of  the  clip  C,  and  the  left  hand  end 
of  the  diagram  touches  the  vertical  limb  of  the  same  clip.  In  an 
indicator  diagram  the  atmospheric  line  is  horizontal.  Now  push  the 
clip  K  towards  the  left  until  its  inner  edge  touches  the  right  hand 
end  of  the  diagram  (in  the  figure  at  0).  Place  the  planimeter  in 
the  position  shown  in  the  figure  with  the  tracing  point  at  0  where 
the  clip  K  touches  the  diagram.  Press  the  head  D  of  the  tracing 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        37 

point  so  as  to  make  a  mark  at  0 ,  and  then  raise  one  of  the  horns 
while  the  graduated  wheel  is  turned  to  zero.  The  outline  of  the 
diagram  is  now  carefully  traced  over  with  the  tracing  point  in  a 
clockwise  direction  until  the  starting  goint  0  is  reached.  Now 
slide  the  tracing  point  along  the  clip  K  (keeping  the  eye  on  the 
rolling  wheel)  until  the  wheel  indicates  zero.  Then  OA  is  the  mean 
height  of  the  diagram  and  by  using  a  scale  graduated  to  represent 
the  scale  of  the  indicator  spring  the  mean  effective  pressure  can  be 
read  off  directly. 

Care  must  be  taken  to  have  the  card  properly  adjusted  as  the 
instrument  mechanically  divides  the  area  traced  by  the  horizontal 
distance  between  the  edges  of  the  clips.  It  is  necessary  that  this 
distance  accurately  represent  the  length  of  the  card. 

Slight  errors  in  the  measurement  of  the  line  OA  are  likely  to 
occur.  When  greater  accuracy  is  desired  it  is  usual  to  read  off 
the  area  of  the  card  on  the  wheel  when  the  pointer  has  returned  to 
0.  The  wheel  with  vernier  is  graduated  to  read  in  square  inches  to 
1/50  square  inch.  In  this  case  it  is  better  not  to  attempt  to  set  the 
wheel  to  zero  before  beginning  to  trace  the  card,  but  note  the  read- 
ing of  the  vernier.  The  difference  in  reading  at  beginning  and  end 
of  the  tracing  will  be  the  required  area.  Dividing  by  the  measured 
length  of  the  card  we  obtain  the  length  of  the  mean  ordinate,  which 
on  multiplying  by  the  scale  of  the  indicator  spring  gives  the  mean 
effective  pressure. 

The  Coffin  instrument  may  be  used  to  measure  the  area  of  any 
figure  that  can  be  placed  in  position  on  the  board.  The  size  and 
shape  of  the  board,  however,  practically  limits  its  use  to  the  meas- 
urement of  indicator  cards,  for  which  it  is  primarily  designed. 

Theory  of  the  Coffin  Planimeter. — Fig.  14  is  a  diagram  repre- 
senting the  instrument,  which,  on  inspection,  is  found  to  be  the 
Amsler  instrument  in  modified  form.  Q  is  the  pivot  moving  in  a 
vertical  line  CQ.  The  arm  m  becomes  infinite.  Continuing  the  com- 
parison CQ  may  be  considered  as  the  circumference  of  the  zero 
circle  whose  radius  is  also  infinite.  The  registering  wheel  D  is 
placed  on  an  axis  parallel  to  arm  I  to  which  it  is  fixed.  It  is  evi- 
dent that  the  exact  position  of  D  is  immaterial,  it  being  placed  so 
as  to  give  the  most  convenient  arrangement.  Suppose  we  make  the 


38 


EXPERIMENTAL  ENGINEERING 


pointer  describe  an  elementary  area  of  height  dx,  bounded  on  one 
side  by  CQ.  The  movement  of  the  wheel  in  and  out  parallel  to 
OE  will  be  equal  in  amount  and  in  opposite  direction,  one  move- 
ment nullifying  the  other.  No  rotation  can  result  from  a  move- 
ment of  the  pointer  along  QC.  There  remains  then  only  the  move- 
ment dx  along  the  line  OX  during  which  the  wheel  moves  also  an 


FIG.  14. 

amount  dx.    The  component  of  this  movement  in  a  direction  tend- 
ing to  rotate  the  wheel  is  dx  cos  0=  — = —  =dR. 

The  elementary  area  is  dA=adx=ldR. 
Integrating  between  0  and  R 

A  =  IR. 
This  expression  is  general,  since  all  areas  may  be  referred  to  CQ. 

The  Coffin  Planimeter  as  an  Averaging  Instrument. — After  de- 
scribing an  area  lying  between  EC  and  OX,  bringing  the  pointer 
back  to  the  original  starting  point,  suppose  we  move  the  pointer 
along  OX  until  the  reading  of  the  wheel  is  again  the  same  as  before 
describing  the  area.  Marking  this  point  A,  it  is  apparent  from  the 
preceding  that  OA  X  OE  will  represent  the  described  area.  If  then 


INSTRUMENTS  FOR  COMPUTING  EXPERIMENTAL  DATA        39 

care  has  been  taken  to  adjust  the  figure  on  the  instrument  so  that 
OE  correctly  represents  its  length,  OA  will  represent  its  mean 
height.  This  property  of  the  instrument  is  made  use  of  in  obtain- 
ing the  mean  height  of  indicator  cards. 

Several  other  planimeters  have  been  devised,  but  in  the  U.  S. 
Navy,  the  Coffin  and  Amsler  instruments  are  generally  employed, 
the  former  for  obtaining  mean  effective  pressures  from  indicator 
cards  and  the  latter  for  measuring  the  areas  of  miscellaneous 
figures. 


CHAPTER  III. 

INSTRUMENTS  FOE  RECORDING  EXPERIMENTAL  DATA. 
Measuring  Machines. 

As  a  basis  for  all  manufacturing  on  the  interchangeable  system, 
means  of  measuring  with  precision  are  imperative.  The  foun- 
dation for  such  a  system  is  a  Standard  Measuring  Machine,  by 
which  existing  gages  can  be  duplicated  and  new  ones  originated  as 
occasion  requires.  With  the  machine  illustrated  in  Fig.  15,  skilled 
mechanics,  accustomed  to  micrometric  work,  will  measure  positively 
to  0.00005  inch,  which  is  the  practical  limit  of  exact  duplication, 
and  variations  of  0.00001  inch  may  be  readily  detected. 

The  Pratt  and  Whitney  Measuring  Machine.  Description.  — 
This  machine,  shown  in  Fig.  15,  has  a  heavy  cast-iron  bed  supported 
by  two  lugs  at  one  end  and  one  at  the  other.  The  bed  is  accurately 
surfaced  in  straight  lines  and  carries  two  head  stocks,  the  one  at 
the  left,  A,  being  rigidly  secured,  and  the  one  at  the  right,  E,  being 
capable  of  movement  along  the  bed.  Each  head  stock  has  a  spindle 
through  it.  The  one  at  the  left,  C,  is  capable  of  movement  in  an 
axial  direction  and  has  a  spring  that  tends  to  keep  it  to  the  right, 
bringing  the  stops  at  D  in  contact.  The  spindle  in  the  moving  head 
stock,  E,  is  moved  in  and  out  by  rotation  of  the  graduated  wheel  F, 
which  operates  a  screw  having  50  threads  to  the  inch.  This  spindle 
carries  an  index  G  which  moves  along  a  scale  reading  to  1/50  inch. 

The  wheel  is  graduated  around  its  circumference,  the  main 
divisions  being  numbered  from  0  to  200,  and  each  main  division 
being  further  divided  into  two  parts.  Movements  of  the  spindle 
can  therefore  be  read  direct  to 


The  end  of  each  spindle  is  squared  off  and  accurately  ground  and 
scraped  to  a  true  surface.  The  moving  head  stock  has  a  clamp  H 
for  securing  it  firmly  in  position.  It  has  also  an  adjusting  screw 
J  for  fine  adjustments.  This  has  another  clamp,  not  seen  in  the 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA       41 

figure,  which  must  be  set  up,  H  being  slacked  off,  when  fine  adjust- 
ments are  to  be  made. 

Attached  to  the  moving  headstock,  is  a  microscope,  K,  with  axis 
vertical,  which  focuses  on  an  index  bar,  not  seen  in  the  figure, 
attached  to  the  rear  side  of  bed  plate.  This  bar  carries  a  series  of 
plugs  with  accurately  surfaced  faces,  on  each  of  which  is  drawn  at 
right  angles  two  intersecting  hair  lines,  the  intersections  being 


FIG.  15. 

spaced  exactly  one  inch  apart.  "Under  the  eye  piece  of  the  micro- 
scope is  an  adjustable  glass,  on  which  is  a  hair  line  drawn  in  a  direc- 
tion perpendicular  to  the  plane  of  the  machine.  The  wheel  L  en- 
ables this  glass  to  be  moved  so  as  to  bring  this  line  into  coincidence 
with  the  crossed  lines  on  the  plugs.  N-N  are  rests  for  holding  in 
position  the  work  that  is  to  be  measured. 

Operation. — To  use  the  machine  it  must  first  be  adjusted  to 
zero.  Eun  the  index  G  to  zero  of  the  linear  scale  at  top  of  head, 
and  bring  the  index  pointer  nearly  to  zero  on  the  graduated  wheel 
F.  Slide  the  head  B  nearly  to  contact  between  the  measuring  faces 


42  EXPERIMENTAL  ENGINEERING 

and  adjust  the  latter  by  means  of  the  adjusting  screw  J  until  the 
drop,  or  indicating  plug,  at  D  shows  a  tendency  to  move.  Then 
clamp  the  head  firmly  and  adjust  F  until  the  drop  plug  falls  into  a 
vertical  position,  but  not  entirely  out  of  contact  with  the  faces  with 
which  it  is  held.  Then  adjust  the  index  for  F  to  zero  by  means  of 
the  screw  M ,  and  bring  the  line  on  glass  under  eye  piece  to  the  zero 
mark  on  the  index  bar. 

The  machine  is  now  adjusted  for  zero  for  its  entire  length,  but 
care  must  be  taken,  not  to  disturb  the  eye-piece  line  for  any  subse- 
quent measurement  of  over  one  inch.  If  there  is  any  doubt  as  to  its 
having  been  moved,  return  to  zero  and  make  sure  of  it. 

To  measure  a  length  greater  than  one  inch,  this  range  being  ob- 
tained by  the  micrometer  screw,  bring  the  head  B  into  range  of  the 
plug  on  index  bar  from  which  the  measurement  is  to  be  taken  and 
adjust  the  line  under  eye  piece  to  coincide  with  mark  on  this  plug, 
using  screw  J  to  make  this  adjustment.  Then  clamp  the  head  and 
proceed.  The  micrometer  screw  should  be  run  out  to  one  inch  if 
the  graduation  on  the  bar  is  less  than  the  amount  to  be  measured, 
and  run  back  to  zero  if  the  graduated  line  is  greater  than  the  length 
required  to  be  measured.  This  will  be  obvious  after  a  few  trials. 

The  pressure  of  contact  is  uniform  at  zero  and  at  any  distance  in 
measurement  of  end  gages,  but  precautions  must  be  taken  to  avoid 
variation  in  temperature  of  the  end  gages,  especially  those  of  con- 
siderable length. 

Flexure  of  the  end  gages  must  also  be  avoided,  and  if  two  sup- 
ports are  used  they  should  be  placed  each  at  about  one  quarter  of  the 
distance  from  each  end. 

Care  of  the  Machine. — Benzine,  used  with  a  soft  woolen  cloth, 
will  clean  the  polished  surfaces  of  the  graduated  plugs  on  the  index 
bar,  and  a  fine  camelVbair  brush  will  afterwards  serve  to  remove 
dust  and  not  scratch  them.  The  use  of  a  fine  grade  of  kerosene 
will  be  useful  to  clean  the  surfaces,  as  it  will  not  rust  them,  and  a 
little  may  be  left  on  them  without  doing  any  injury  or  preventing 
the  clear  definition  of  the  lines  at  any  time. 

The  microscope  must  be  clamped  in  place  with  each  adjustment. 
It  must  be  removed  in  order  to  place  the  covers  over  the  index  bar. 
On  replacing  it,  it  must  be  readjusted  for  zero. 


INSTRUMENTS  FOR  RECORDING  EXPERIMENTAL  DATA       43 

Measurement  of  Pressure. 

Fluid  pressures  are  commonly  measured  by  some  form  of  gage 
in  which  the  laws  of  deformation  of  elastic  material  are  made 
use  of.  Such  gages  are  of  two  kinds,  pressure  gages,  which  record 
pressures  above  the  atmosphere,  and  vacuum  gages,  which  record 
pressures  below  the  atmosphere.  In  America  and  England,  pressure 
gages  are  graduated  to  record  pressures  in  pounds  per  square  inch, 


FIG.  16. 

except  for  very  heavy  pressures  which  are  sometimes  recorded  in 
atmospheres.  Vacuum  gages  register  the  difference  between  the 
atmospheric  pressure  and  the  pressure  in  the  vessel  to  which  at- 
tached. They  are  graduated  to  show  this  difference  in  inches  of 
mercury.  This  system  has  been  adopted  to  facilitate  comparison 
with  the  barometer,  which  is  read  in  inches  of  mercury.  The  dif- 
ference between  barometer  and  vacuum  gage  readings  gives  the 
absolute  pressure  in  inches  of  mercury  in  the  vessel  to  which  the 
vacuum  gage  is  attached.  One  cubic  inch  of  mercury  weighs  0.49 
pounds.  Hence  to  convert  inches  of  mercury  into  pounds  per  square 
inch,  multiply  by  0.49. 


44 


EXPERIMENTAL  ENGINEERING 


Pressure  gages  and  vacuum  gages  are  similar  in  construction. 
They  are  of  two  general  types,  (1)  the  diaphragm  gage,  one  of 
which  is  shown  in  Fig.  16,  and  (2)  the  bent  tube  or  Bourdon  gage, 
shown  in  Fig.  17.  In  the  first  of  these  types  the  diaphragm  is  in 
equilibrium  under  atmospheric  pressure.  If  pressure  be  applied  to 
either  side  it  is  deflected  an  amount  proportional  to  the  pressure 
applied.  This  deflection  causes  a  movement  of  the  attached  strut, 
which  is  communicated  through  the  connections  shown,  to  the  cen- 
tral spindle,  carrying  an  index  that  moves  around  a  graduated  dial. 


FIG.  17. 

In  the  second  type,  there  is  a  flattened  tube  communicating 
with  the  fluid  under  pressure.  If  the  pressure  be  increased,  it  tends 
to  round  out  the  flattened  section,  and  thus  tends  to  straighten  the 
tube.  Fig.  17  shows  a  single  tube  gage,  in  which  the  end  of  tube  is 
connected  through  levers  with  a  sector  that  gears  with  a  pinion  on 
the  spindle-carrying  index  as  before.  If  this  tube  be  opened  to  a 
vacuum,  it  will  tend  to  still  further  flatten,  and  the  ends  will  tend 
to  come  closer  together,  with  the  reverse  movement  of  index  over 
dial.  The  same  construction  is  therefore  used  for  both  pressure  and 
vacuum  gages. 

The  double  tube  gage,  shown  in  Fig.  18,  is  of  similar  con- 
struction, except  that  both  ends  of  the  tube  are  free  to  move,  and 
the  actuating  mechanism  for  the  index  is  suspended  between  them. 


INSTRUMENTS  FOR  KECORDING  EXPERIMENTAL  DATA       45 

The  connection  for  introducing  the  pressure  is  in  the  middle  of  the 
tube,  which  is  secured  in  place.  This  form  of  gage  has  the  advan- 
tage that  the  tube  may  be  drained  completely  when  the  pressure  is 
.off,  which  gives  it  somewhat  greater  durability. 

A  Compound  Gage  is  often  used  for  receivers,  jackets,  or  other 
places  where  the  steam  pressure  is  sometimes  above  and  sometimes 
below  the  atmosphere.  The  0  indicates  atmospheric  pressure.  The 
dial  is  graduated  to  the  right  of  the  0  for  pressures  above  the  at- 
mosphere in  pounds  per  square  inch,  and  to  the  left  of  the  0  for 


FIG.  18. 

pressures  below  the  atmosphere  in  inches  of  mercury.  It  will  be 
noted  that  on  a  simple  vacuum  gage,  the  connections  are  such  that 
the  index  moves  to  the  right,  but  on  a  compound  gage,  when  regis- 
tering vacuum,  the  index  moves  to  the  left. 

Recording  Pressure  Gage. — There  are  several  forms  of  this 
apparatus,  in  all  of  which  the  principle  of  operation  is  the  same. 
The  mechanism  for  registering  the  pressure  is  similar  to  that  in  an 
ordinary  gage,  but  the  moving  index  is  longer,  and  the  spring  is 
stiffer,  so  that  the  limit  of  pressure  is  recorded  in  a  comparatively 
small  arc  of  the  circle  swept  by  the  index.  The  end  of  index  carries 
a  pen  or  pencil,  and  the  pressure  is  recorded  on  a  sheet  of  paper  that 
receives  motion  from  a  clock  mechanism.  The  paper  is  laid  off  and 
marked  for  intervals  of  time  in  one  direction  and  for  intervals  of 


46 


EXPERIMENTAL  ENGINEERING 


pressure  in  the  other.  The  apparatus  then  gives  a  continuous  record 
of  the  pressure  on  the  gage.  In  some  forms  of  the  apparatus,  where 
the  paper  is  unwound  from  a  spool,  this  record  continues  for  several 
days  on  the  same  sheet  of  paper.  In  other  forms,  as  in  that 
described  below,  the  paper  must  be  changed  every  24  hours. 


FIG.  19. 


Bristol's  Recording  Pressure  Gage. — As  used  in  recording  pres- 
sures in  pounds  per  square  inch,  this  is  to  be  seen  in  the  labora- 
tory, as  shown  in  Fig.  19.  The  recording  mechanism  contains  a 
flattened  tube,  similar  to  that  of  the  single  tube  Bourdon  gage,  ex- 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA       47 

cept  that  it  is  wound  in  a  spiral,  and  the  pressure  when  applied 
causes  it  to  unwind  to  an  extent  proportional  to  such  pressure.  The 
index  is  carried  from  the  end  of  the  spiral  and  has  a  pen  attached  to 
its  free  end.  This  traces  a  line  on  the  revolving  paper  dial  which 


FIG.  20. 


gives  a  continuous  record  of  the  pressure.  The  paper,  when  placed 
on  the  apparatus,  is  adjusted  so  as  to  bring  the  time,  as  marked  on 
the  paper  for  the  instant  of  making  such  adjustment,  under  the  pen. 
This  dial  will  then  be  good  for  24  hours,  when  it  must  be  removed, 


48 


EXPERIMENTAL  ENGINEERING 


and  is  then  marked  with  the  date  and  any  other  data  that  it  may 
be  desirable  to  record. 

Fig.  20  shows  another  form  of  the  same  apparatus,  used  for 
recording  air  pressures.     The  tube  is  bellows-shaped  and  its  tend- 


FIG.  21. 

ency  to  elongate  is  resisted  by  a  metal  strip  on  one  side.  The  pen 
arm  is  attached  directly  to  this  diaphragm  tube  and  pressures  are 
recorded  on  a  dial  in  the  same  manner  as  before. 

Fig.  21  shows  the  exterior  of  the  gage,  with  the  form  of  dial  used 
to  give  the  continuous  record. 


INSTRUMENTS  FOR  RECORDING  EXPERIMENTAL  DATA       49 

Uehling  Differential  Pressure  Eecorder. — The  working  principle 
of  the  Uehling  Differential  Pressure  Eecorder  includes  a  gravity 
U  tube,  AEB,  Fig.  22.  B  is  suspended  by  a  rod  M  from  a  bell  float 
I  which  is  buoyed  by  mercury  contained  in  a  cylindrical  vessel  J. 
M  passes  freely  through  a  central  tube  H  and  in  front  of  the  record- 
ing paper  which  is  fed  by  clock  work  and  kept  taut  by,  and  auto- 
matically wound  on,  a  receiving  roller  T.  A  small  horse-shoe  mag- 
net N  pivoted  on  a  bracket  fastened  to  rod  M  serves  as  a  pen  holder. 
The  pen  is  kept  to  the  paper  by  the  magnetism  of  the  horse  shoe 
acting  on  a  narrow  iron  strip  'P.  B  is  connected  to  A  and  D  by 
means  of  flexible  tubes  E  and  F.  F  communicates  with  the  top  of 
floating  chamber  B  through  C,  and  E  with  the  bottom  of  said 
chamber  as  shown.  Z  is  an  equalizing  tube  controlled  by  cock  X. 
W  connects  with  the  lower  and  Y  with  the  higher  pressure. 

Connections  having  been  made,  for  example,  with  a  Venturi  or 
Pitot  meter;  open  X  then  open  W  and  Y.  The  pressure  will  be 
equalized  through  Z  and  the  mercury  in  A  and  B  will  stand  at  the 
same  level;  B  carrying  the  major  part  of  the  mercury  will  pull 
down  the  bell  float  until  the  weight  of  mercury  displaced  by  the 
latter  equals  the  weight  of  B  with  its  mercury  content  and  connec- 
tions. When  equilibrium  is  thus  established,  the  pen  will  point  to 
the  zero  line.  Closing  X  the  higher  pressure  will  be  confined  to  D, 
the  lower  pressure  to  A,  and  in  consequence  mercury  will  be  driven 
from  B  to  A  until  the  pressure  difference  is  balanced  by  the  mercury 
head  in  A.  As  mercury  flows  from  B  to  A  the  weight  suspended  by 
M  diminishes  and  the  bell  float  rises,  carrying  with  it  the  pen  and 
also  chamber  B.  As  the  pressure  difference  diminishes,  the  mercury 
returns  to  B,  its  weight  increases  and  the  reverse  movement  takes 
place. 

The  cross  sectional  areas  of  the  stationary  leg  A,  the  floating  leg 
B  and  the  bell  float  I  are  so  related  that  the  pen  will  move  over  the 
entire  scale  covering  the  available  width  of  the  chart  for  any  pre- 
determined pressure  difference  to  be  recorded. 

This  instrument  can  be  calibrated  to  record  pressure  differences 
from  0  to  1  inch,  to  from  0  to  30  inches  of  mercury  head  or  more, 
under  a  total  pressure  of  200  Ibs.  and  over.  In  all  cases  the  calibra- 
tion on  chart  covers  3  inches  in  width. 


50 


EXPERIMENTAL  ENGINEERING 


FIG.  22. 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA        51 

The  recorder  can  be  conveniently  fastened  to  any  wall  or  column. 
It  makes  a  continuous  rectilinear  record  of  pressure  differences  or 
rate  of  flow  of  either  liquids  or  gases.  Used  in  connection  with  a 
Venturi  or  Pitot  meter  described  in  Chapter  VI,  it  may  be  cali- 
brated to  record  cubic  feet  per  hour  or  other  units  as  may  be  desired. 

Testing  Pressure  Gages. — Fig.  23  shows  a  late  form  of  appara- 
tus for  testing  gages,  as  made  by  Messrs.  Schaeffer  &  Budenberg  and 
installed  in  the  laboratory.  It  is  in  two  parts,  for  testing  pressure 
gages  and  vacuum  gages.  On  the  left  is  the  arrangement  for  test- 
ing pressure  gages.  Pressure  is  applied  by  means  of  a  screw 
plunger,  that  is  worked  in  and  out  in  a  cylindrical  chamber  by  means 
of  the  hand  wheel  shown  at  the  extreme  left.  A  reservoir,  contain- 
ing oil  or  glycerine,  connects  with  this  chamber  through  the  valve  A. 
Valve  B  connects  the  chamber  with  a  vertical  cylinder,  in  which  is 
an  accurately  fitting  piston  of  14  square  inch  area  of  cross  section. 
This  piston  carries  a  tray  on  which  the  disc-shaped  weights,  shown 
at  the  back,  are  placed  for  directly  measuring  the  applied  pressure. 
The  tray  and  piston,  together,  weigh  li/4  pounds,  so  that  when  bal- 
anced, without  the  addition  of  weights,  the  pressure  per  square  inch 
in  chamber  is  5  pounds.  A  pipe  connects  the  chamber  with  the 
mountings  shown  at  the  front,  on  which  gages  may  be  placed.  The 
gage  under  test  is  mounted  at  the  left,  the  valve  C  serving  to  shut 
off  or  turn  on  the  pressure.  The  mounting  at  the  right,  to  which 
pressure  is  admitted  through  the  valve  D,  is  for  a  standard  gage, 
but  may  be  used  for  ordinary  testing  work,  in  which  case  two  gages 
may  be  tested  at  once. 

Operation. — To  test  a  gage,  the  connection  to  reservoir  is  opened 
and  all  other  connections  are  shut  off.  The  plunger  is  forced  in  its 
full  length  and  the  reservoir  is  filled  with  oil.  Then  the  plunger 
is  withdrawn  as  far  as  it  will  go  in  the  chamber,  and  the  connection 
to  reservoir  is  shut  off.  The  gage  for  test  is  mounted,  its  connecting 
valve  is  opened,  and  the  piston  for  carrying  weights  is  put  in  place. 
Opening  the  valve  under  the  piston,  weights  are  added  to  the  tray 
in  increments  of  5  or  10  pounds,  and  pressure  applied  by  forcing 
in  the  plunger  until  the  piston  lifts,  each  time  a  weight  is  added. 
To  prevent  piston  or  index  sticking,  the  piston  is  spun  around  each 
time  the  gage  is  read,  thus  ensuring  a  correct  reading. 


52  EXPERIMENTAL  ENGINEERING 

In  case  the  gage  is  found  to  read  incorrectly,  the  index  should 
be  removed  and  properly  set.     In  cheaply  constructed  gages  a  dif- 


FIG.  23. 


ferent  error  will  sometimes  be  found  at  low  and  at  high  pressures. 
In  such  cases  the  correction  should  be  made  at  the  average  pressure 
for  which  the  gage  is  to  be  used. 


INSTRUMENTS  FOR  BECORDING  EXPERIMENTAL  DATA        53 

Where  many  gages  are  to  be  tested  at  the  same  time,  it  will  be 
found  most  convenient  to  first  test  the  "  standard  "  gage,  then  shut 
off  the  vertical  cylinder  and  compare  the  readings  of  the  other  gages 
with  the  "  standard."  A  standard  gage  should,  however,  never  be 
relied  upon,  unless  tested  immediately  before  or  after  using. 

Testing  Vacuum  Gages. — The  apparatus  at  the  right  in  Fig. 
23  is  for  testing  vacuum  gages.  A  vacuum  pump  at  the  extreme 
rights  connects  through  cock  F  with  a  mercury  column  and  through 
valve  E  with  the  mounting  on  which  the  gage  to  be  tested  is  placed. 

Testing  Gages  on  Board  Ship. — The  above  apparatus  is  some- 
times supplied  to  large  vessels.  The  usual  form  of  apparatus  sup- 
plied is  similar  to  that  described  for  testing  pressure  gages,  but  in 
a  light  portable  form  with  the  vacuum  pump  omitted.  Its  opera- 
tion is  the  same  as  that  of  the  larger  apparatus. 

Vacuum  gages  on  board  ship  are  usually  tested  by  comparison 
with  one  another.  If  a  more  accurate  test  is  desired  and  no  means 
are  supplied  for  conducting  such  test,  they  may  be  taken  ashore  for 
this  purpose  at  a  navy  yard  at  frequent  intervals. 

Manometers. — This  name  is  applied  to  a  gage  used  to  register  a 
difference  between  two  pressures,  usually  where  the  difference  is 
small.  Such  gages  are  used  to  show  the  air  pressure  in  a  closed  fire 
room,  or  the  draft  pressure  in  a  flue  passage,  where  the  difference 
between  the  variable  pressure  and  the  atmospheric  pressure  is  ob- 
served. The  common  form  of  manometer  is  a  U-shaped  glass  tube, 
partially  filled  with  water,  one  leg  of  which  is  connected  to  the  body 
of  air  or  gas,  the  pressure  of  which  is  to  be  measured,  and  the  other 
leg  is  connected  to  the  atmosphere.  A  scale  shows  the  difference  in 
height  of  the  water  in  the  two  legs  of  the  tube,  and  thus  indicates 
the  pressure  in  inches  of  water.  For  indicating  slightly  greater 
pressures,  a  mercury-filled  manometer  is  sometimes  used,  in  which 
the  indication  is  of  course  in  inches  of  mercury. 

Measurement  of  Temperature. 

Ordinary  temperatures  of  water  and  steam  are  measured  by  means 
of  mercurial  thermometers.  Before  proceeding  with  any  experi- 
ment requiring  accuracy,  such  thermometers  should  be  carefully 
calibrated,  unless  they  are  standard  thermometers  of  known  ac- 


54  EXPERIMENTAL  ENGINEERING 

curacy.  The  bulb  of  the  thermometer  and  so  much  of  the  stem  as  is 
ordinarily  immersed  in  the  liquid  whose  temperature  is  to  be  taken, 
is  packed  in  melting  ice  and  after  the  mercury  becomes  stationary 
the  reading  is  taken.  It  is  again  placed  in  a  vessel  of  boiling  water 
that  is  open  to  the  atmosphere  and  the  reading  again  taken.  Eead- 
ings  are  thus  obtained  at  the  known  temperature  of  32°  and  212° 
on  the  Fahrenheit  scale  or  0°  and  100°  on  the  Centigrade  scale. 
From  these  the  proper  corrections  are  derived  to  be  applied  to  any 
thermometer  reading.  It  is  usual  to  assume  that  the  scale  of  the 
thermometer  is  constant  above  the  boiling  point  to  the  limit  of  the 
tube.  For  this  to  be  true  it  is  necessary  that  the  area  of  cross 
section  of  the  tube  should  be  constant. 

High  Temperatures.  Pyrometry. — Mercury  boils  at  675°  F., 
under  atmospheric  pressure.  It  becomes  necessary  to  resort  to  ap- 
paratus other  than  the  ordinary  mercurial  thermometer  for  the 
measurement  of  temperatures  above  about  500°  F.  Such  instru- 
ments are  known  as  high  temperature  thermometers  or  pyrometers. 
Several  different  types  have  been  constructed  as  follows : 

Gas  thermometers. 

Pneumatic  pyrometers. 

Mercurial  pyrometers. 

Expansion  pyrometers. 

Calorimetric  pyrometers. 

Thermo-electric  pyrometers. 

Eesistance  thermometers. 

Eeflecting  pyrometers. 

The  Gas  Thermometer. — This  is  used  as  the  standard  by  which  to 
calibrate  all  other  high  temperature  thermometers,  and  for  research 
work  where  great  accuracy  is  required.  It  is  not  suited  for  ordinary 
experimental  work  on  account  of  its  lack  of  portability  and  its 
high  cost. 

Instruments  of  this  type  are  usually  specially  constructed  for  the 
service  that  is  required,  but  the  principle  of  operation  in  all  such 
instruments  is  the  same.  The  relation  between  pressure  volume 
and  temperature  of  a  gas  follows  the  law  PV  =  CT,  where  P  is  the 
absolute  pressure,  V  is  the  specific  volume,  C  is  a  constant  and  T  is 
the  absolute  temperature.  A  large  bulb  is  constructed  to  contain 


INSTRUMENTS  FOR  KECORDING  EXPERIMENTAL  DATA        55 


56 


EXPERIMENTAL  ENGINEERING 


a  fixed  volume  of  gas.  Various  materials  have  been  used  for  the 
bulb,  but  the  best  results  are  obtained  with  bulbs  of  platinum,,  or 
where  very  high  temperatures  are  to  be  measured,  of  an  alloy  of 


FIG.  25. 

platinum  and  iridium.     Air  and  hydrogen  have  been  used  in  the 
bulb,  but  the  best  results  have  been  obtained  with  nitrogen. 

The  bulb  being  subjected  to  heat,  the  rise  in  temperature  is 
measured  by  the  rise  in  pressure  of  the  gas.  This  is  registered  on  a 
gage,  graduated  to  read  the  degrees  rise  in  temperature. 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA        57 

The  Industrial  Thermograph  is  a  practical  instrument  based  on 
the  principle  of  the  gas  thermometer.  The  general  appearance  of 
the  instrument  is  shown  in  Fig.  24,  while  the  moving  element  is 
shown  in  Fig.  25.  There  is  a  metallic  bulb,  connected  by  very  fine 
copper  tubing  with  the  coiled  tube  shown  in  Fig.  25.  Instruments 
on  this  principle  are  constructed  for  all  ranges  of  temperature  up 
to  about  1000°  F.  In  instruments  made  for  temperatures  below  50° 
the  bulb  is  filled  with  alcohol  and  the  long  capillary  tube  is  omitted, 
the  bulb  being  placed  close  to  the  pressure  tube.  For  instruments 
having  a  range  between  50°  and  about  500°  sulphur  dioxide  (S02) 
is  the  medium  employed,  while  for  instruments  intended  for  a 
range  above  400°  the  bulb  is  filled  with  nitrogen,  making  the  in- 
strument in  this  case  a  true  gas  thermometer.  The  recording  gage 
shown  in  the  figure  may  be  replaced  with  an  indicating  gage.  In 
any  case  the  gage  is  graduated  for  degrees  rise  in  temperature. 

TTehling's  Pneumatic  Pyrometer. — The  underlying  principle  of 


B 


FIG.  26. 


this  instrument  is  based  on  the  same  law  that  governs  the  opera- 
tion of  the  gas  thermometer.  It  is  illustrated  diagrammatically  in 
Fig.  26.  A  small  steam  aspirator,  working  at  a  uniform  rate, 
draws  air  through  the  apertures  A  and  B,  causing  a  partial  vacuum 
in  chambers  C  and  D.  The  same  amount  of  air  must  necessarily 
pass  through  each  aperture.  If  A  and  B  are  the  same  size,  and  if 
the  air  remains  at  a  fixed  temperature  during  a  given  length  of 
time,  the  suction  in  chamber  C  will  be  practically  twice  that  in 


58  EXPERIMENTAL  ENGINEERING 

chamber  D.  If,  however,  this  air  is  heated  when  it  passes  through 
A,  but  again  cooled  to  a  lower  fixed  temperature  before  it  passes 
through  B,  the  specific  volume  will  be  higher  on  passing  through  B 
and  therefore  the  pressure  in  C  will  be  lower.  In  the  same  way  any 
change  in  temperature  of  the  air  flowing  through  A  will  have  its 
influence  on  the  amount  of  vacuum  in  chamber  D.  Thus  the  ma- 
nometer tube  P  may  be  calibrated  to  indicate  the  temperature  of 
the  air  passing  through  A. 

Fig.  27  shows  a  diagrammatic  disposition  of  all  the  parts  com- 
bined in  the  complete  instrument. 

The  interior  of  the  pipe  e,  f,  g,  li,  i  from  aperture  to  aperture,  to- 
gether with  the  branches  q  and  s,  constitute  the  chamber  C  of  Fig. 
26.  Its  inlet  from  the  atmosphere  is  through  the  opening  a  at  the 
bottom  of  filter  I,  and  its  connection  with  chamber  C'  is  through  the 
pipe?. 

The  aspirator  D  exhausts  into  the  chamber  G,  keeping  it  at  a 
constant  temperature  of  212°.  The  steam  and  condensed  water, 
together  with  the  air  drawn  through  the  aperture,  escape  through 
the  pipe  t  at  atmospheric  pressure.  Opening  the  valve  6  steam 
enters  the  aspirator  D,  and  sucks  the  air  through  the  tube  m,  out  of 
the  chamber  C'  and  produces  a  suction,  which  is  kept  constant  by 
the  regulator  H,  as  shown  by  the  manometer  p.  With  a  constant 
suction  in  C'  and  cocks  2  and  4  open,  air  will  enter  at  a,  pass 
through  the  filter  I,  where  it  is  purified,  then  through  the  connec- 
tion b  into  the  fire  tube.  It  flows  forward  in  the  annular  space 
between  the  two  tubes  c  and  f;  as  soon  as  it  reaches  the  platinum 
tube  d,  which  protrudes  from  the  cooler,  it  becomes  heated  and 
enters  through  the  aperture  A  into  the  chamber  C,  at  the  tempera- 
ture surrounding  the  exposed  end  of  the  fire  tube,  which  is  the  tem- 
perature to  be  measured.  After  passing  A,  the  air  flows  through  the 
pipe  e,  f,  g,  h  into  the  coil  i,  where  it  assumes  the  temperature  of 
212°,  at  which  it  passes  through  aperture  B,  thence  by  the  connec- 
tion I  into  the  chamber  C",  from  which  it  is  drawn  by  the  aspirator 
D  through  m,  and  discharged  with  exhaust  steam  and  condensed 
water. 

The  branch  pipes  s  and  q'  connect  respectively  with  the  recording 
gage  L,  and  the  manometer  q,  which  is  placed  in  proximity  to  the 
temperature  scale,  as  shown. 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA        59 


H 


PIG.  27. 


60  EXPERIMENTAL  ENGINEERING 

This  combination,  therefore,  fulfils  all  the  conditions — viz.,  air 
is  drawn  through  the  instrument  by  a  constant  suction.  It  passes 
through  aperture  B  at  a  constant  temperature.  Aperture  A  is  so 
located  that  the  air  must  enter  at  the  temperature  to  be  measured, 
hence  the  indication  of  the  manometer  q  will  vary  with  the  tem- 
perature at  A ,  as  we  have  demonstrated,  and  can  be  read  off  directly 
on  the  temperature  scale  placed  beside  the  same. 

Fig.  29  shows  the  instrument  complete,  with  recording  gage  and 
with  portable  fire  tube.  The  fire  tube  is  shown  in  section  in  Fig. 
28.  The  aperture  A  of  the  diagram  is  located  near  the  closed  end 
of  a  small  platinum  tube  e,  placed  within  a  larger  tube  d,  which  is 
also  of  platinum  with  closed  end.  Both  d  and  e  are  brazed  into 
drawn  copper  tubes  c  and  /,  and  these  tubes  are  surrounded  by  a 
water  jacket  F.  Before  entering  aperture  A  the  air  is  drawn 
through  the  cotton  filter  and  through  the  annular  space  between 
tubes  d  and  e,  where  it  reaches  the  temperature  to  be  measured. 

Connections  to  the  fire  tube  may  be  made  of  flexible  tubing,  thus 
enabling  the  tube  to  be  inserted  successively  into  different  furnaces 
within  a  range  of  150  feet. 

This  instrument  is  accurate  and  durable  and  has  a  temperature 
range  up  to  about  3000°  F.  While  the  fire  tube  is  portable,  the 
instrument  itself  must  be  set  up  permanently  and  for  this  reason 
it  is  not  well  adapted  to  ordinary  marine  work. 

Mercurial  Pyrometer. — This  is  similar  to  the  ordinary  mercurial 
thermometer  in  that  there  is  a  bulb  and  tube  filled  with  mercury, 
but  the  space  in  tube  above  the  mercury  is  filled  with  nitrogen. 

As  the  tube  is  heated  the  mercury  expands  and  compresses  the 
nitrogen,  the  resultant  increase  in  pressure  on  the  mercury  raising 
its  boiling  point.  These  pyrometers  are  made  in  both  portable  and 
stationary  form.  The  end  which  contains  the  nitrogen  may  take 
the  ordinary  form  of  a  mercurial  thermometer,  or  may  terminate 
in  a  pressure  gage  calibrated  in  degrees  of  temperature.  The  latter 
form  of  instrument  is  more  easily  read  and  a  recording  gage  may 
be  fitted  from  which  a  chart  can  be  taken  showing  the  temperature 
changes  throughout  each  twenty-four  hours.  In  Fig.  30  is  shown 
a  typical  mercurial  pyrometer  with  recording  gage  and  flexible  tube 
connection. 


INSTRUMENTS  FOR  RECORDING  EXPERIMENTAL  DATA        61 


EXPERIMENTAL  ENGINEERING 


FIG.  29. 


INSTRUMENTS  FOR  KECORDING  EXPERIMENTAL  DATA 


63 


Mercurial  pyrometers  are  fairly  accurate,  and  are  particularly 
adapted  to  measuring  uptake  and  chimney  temperatures.  They  are 
constructed  to  read  as  high  as  1000°  F. 

Expansion  Pyrometers. — The  difference  in  the  rate  of  lineal  ex- 
pansion of  two  metals  is  the  principle  upon  which  expansion  pyrom- 
eters are  based.  For  the  same  rise  in  temperature,  copper  expands 


FIG.  30.— Mercurial  Pyrometer  with  Recording  Gage. 

60  per  cent  more  than  iron.  In  the  expansion  pyrometer  a  tube  of 
copper  is  inclosed  in  a  tube  of  iron.  At  the  end  to  be  heated  the 
tubes  are  securely  fastened  to  each  other.  At  the  other  end  they  axe 
attached  to  a  set  of  multiplying  gears  which  actuate  a  needle  pointer 
over  the  face  of  a  properly  calibrated  dial.  It  is  necessary  to  expose 
the  entire  length  of  the  expansion  tubes  to  the  full  effect  of  the  heat 
to  be  measured;  if  this  is  not  accomplished,  error  will  result  as  the 
proper  amount  of  elongation  has  not  been  obtained.  When  the 


64  EXPERIMENTAL  ENGINEERING 

pyrometer  is  first  inserted,  the  pointer  will  act  rapidly  in  one  direc- 
tion or  the  other  and  give  an  untrue  reading  temporarily.  This  is 
caused  by  the  outer  tube  heating  and  expanding  more  rapidly  than 
the  inner  one.  As  soon  as  the  inner  tube  heats  up  and  expands 
proportionately,  the  pointer  will  correctly  indicate  the  temperature. 


FIG.  31. — Expansion  Pyrometer. 

When  an  expansion  pyrometer  has  been  used  repeatedly  for  tem- 
peratures near  its  limit,  the  indicator  will  no  longer  return  to  the 
position  indicating  the  temperature  of  the  atmosphere.  A  perma- 
nent change  has  taken  place  in  the  length  of  one  of  the  tubes.  By 
loosening  a  set  screw  the  dial  may  be  adjusted  to  correct  the  varia- 
tion. 


INSTRUMENTS  FOR  RECORDING  EXPERIMENTAL  DATA        65 

A  standard  type  of  expansion  pyrometer  is  shown  in  Fig.  31. 
In  spite  of  the  fact  that  these  pyrometers  get  out  of  calibration 
rather  easily  they  are  capable  of  giving  close  results  if  understood 
and  carefully  handled.  They  will  indicate  temperatures  as  high  as 
1500°  F. 

Calorimetric  Pyrometers. — The  method  of  indicating  temperature 
by  the  calorimetric  pyrometer  is  the  reverse  of  that  used  in  de- 
termining specific  heats  by  the  water  calorimeter. 

A  given  weight  of  some  metal,  the  specific  heat  of  which  is  known, 
is  heated  to  the  temperature  to  be  measured  and  then  instantly 
plunged  into  a  known  weight  of  water.  The  rise  in  temperature  of 
the  water  is  noted.  The  formula  for  finding  the  temperature  is : 

x=T+wt 

ws 
in  which, 

X  =  Temperature  to  be  measured  in  degrees  Fahrenheit; 
T=  Final  temperature  of  the  water; 
W= Weight  of  the  water  in  pounds; 
£=Rise  in  temperature  of  the  water; 
w— Weight  of  the  metal,  in  pounds; 
s  —  Specific  heat  of  the  metal. 

A  calorimetric  pyrometer  is  an  apparatus  by  means  of  which  the 
temperature  may  be  found  without  using  each  time  the  formula 
previously  given.  It  usually  consists  of  a  copper  cup  which  is  in- 
sulated to  prevent  loss  from  radiation  and  which  has  gage  marks 
upon  it  for  a  definite  amount  of  water.  Fastened  to  the  cup  and  so 
arranged  as  to  be  properly  immersed,  is  a  small  thermometer.  A 
sliding  scale  is  attached  to  the  thermometer.  A  copper  or  platinum 
ball  completes  the  outfit.  The  scale  on  the  thermometer  is  calibrated 
with  the  quantity  of  water  which  the  instrument  holds  and  with 
the  metal  ball  so  that  the  rise  in  temperature  of  the  water  causes 
the  thermometer  to  indicate  correctly  the  temperature  being 
measured. 

This  pyrometer  is  very  liable  to  inaccuracy.  The  results  which  it 
gives  vary  with  the  skill  and  care  used  in  its  manipulation.  Its 
cheapness  and  portability,  however,  recommend  it  where  approxi- 
mate results  are  satisfactory.  It  may  be  used  for  temperatures  up 
to  3000°  F. 


66  EXPERIMENTAL  ENGINEERING 

Thermo-Electric  Pyrometers. — When  rods  or  wires  of  two  dis- 
similar metals  are  joined  at  one  end,  they  compose  a  thermo-electric 
"  couple  "  or  "  element."  When  the  junction  is  heated,  a  difference 
of  electrical  pressure  is  established  between  the  cool  ends.  If  a 
circuit  is  made  by  joining  the  cool  ends  together,  either  directly  or 
b}r  means  of  a  conductor,  a  current  will  flow.  The  strength  of  the 
current  depends  upon  the  nature  of  the  "  element "  and  the  dif- 
ference in  temperature  between  the  hot  junction  and  the  cool  ends 
or  cold  junction.  The  deflection  of  a  galvanometer  placed  in  the 
circuit  may  be  calibrated,  then,  to  indicate  the  temperature  at  the 
hot  junction. 


FIG.  32. 

A  thermo-electric  pyrometer  consists  of  the  thermo-electric  couple, 
the  galvanometer  and  a  device  for  compensating  for  the  changes  in 
temperature  at  the  cold  junction.  The  hot  junction  is  protected 
by  a  fire-proof  insulation  of  asbestos  and  carborundum,  and  the 
whole  is  encased  in  a  common  iron  pipe  for  further  protection.  In 
most  makes  for  commercial  use,  the  change  in  temperature  of  the 
cold  junction  is  taken  care  of  by  shifting  the  scale  on  the  galva- 
nometer a  few  degrees  one  way  or  the  other  when  the  temperature 
at  the  cold  junction  is  observed  to  change  appreciably.  Fig.  32 
shows  a  thermoelectric  pyrometer  outfit  of  the  usual  type.  A  re- 
cording device  is  sometimes  added. 

Thermo-electric  pyrometers  are  adaptable  to  many  uses.  With 
proper  handling  they  will  give  accurate  results.  Their  great  ad- 
vantages are  convenience  and  simplicity.  Repeated  reheating  will 
cause  the  potential  of  the  thermo-electric  couple  to  change,  necessi- 
tating frequent  recalibration  and  an  occasional  renewal  of  the 
couple.  Where  high  temperatures  are  measured  and  continuous 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA        67 

service  required,  the  cost  of  upkeep  may  be  considerable.  Depend- 
ing on  the  composition  of  the  thermo-electric  element,  these  pyrom- 
eters will  measure  temperatures  up  to  3000°  F. 

For  temperatures  up  to  1100°  F.,  the  element  is  made  of  nickel 
and  constantan,  a  composition  consisting  of  60%  copper  and  40%' 
nickel.  For  temperatures  ranging  between  1100°  and  2300°  F., 
nickel  and  a  special  carbon  are  used,  and  for  higher  temperatures 
up  to  3000°  F.,  platinum  and  an  alloy  consisting  of  90%  plati- 
num and  10%  rhodium  or  iridium  make  up  the  element. 

Resistance  Thermometers. — The  electrical  resistance  of  pure 
platinum  varies  directly  with  its  temperature.  This  property  is 
made  use  of  in  the  measurement  of  high  temperatures  where  the 
problem  becomes  one  of  measuring  the  electrical  resistance  of  a 
piece  of  platinum  wire,  heated  to  the  temperature  under  investi- 
gation. 

A  coil  of  platinum  wire  is  wound  in  crossed  layers  of  mica  and 
then,  with  the  lead  wires,  is  encased  in  a  porcelain  tube  which  pro- 
tects the  wires  and  holds  them  in  position.  The  tube,  with  its  con- 
tents, is  known  as  the  ~bul~b  and  is  shown  in  section  in  Fig.  33. 


FIG.  33. 

Fig.  34  shows  a  diagram  of  the  electrical  connections  in  the 
apparatus.  A,  B,  and  C  correspond  to  the  three  contact  points  on 
the  head  of  the  bulb.  R  is  a  fixed  resistance  which  at  normal  tem- 
perature corresponds  to  the  resistance  of  the  platinum  coil,  rr 
are  fixed  and  equal  resistances,  yy  are  the  resistances  of  the  two 
lead  wires.  These  are  equal  and  may  be  taken  as  negligible  in  the 
following  explanation  of  the  principles  of  the  instrument.  DE  is 
a  wire,  of  uniform  section  and  having  a  resistance  L,  joining  the 
two  resistances  rr.  It  is  connected  by  a  sliding  contact  F  through 
the  battery  G  to  C. 

Let  x=ihe  resistance  of  the  platinum  coil,  varying  under  change 
of  temperature. 

Let  z  =  the  resistance  of  DF. 


68 


EXPERIMENTAL  ENGINEERING 


It  will  be  noted  that  the  diagram  is  that  of  a  Wheatstone  bridge, 
in  which  the  balance  is  produced  by  varying  the  position  of  the 
sliding  contact  F  on  the  wire  DE.  From  this  we  see  that 


R 


r  +  z 


(r+z) 


FIG.  34. 
For  the  minimum  reading  of  the  thermometer,  z  —  L  and 


For  the  maximum  reading,  2  =  0  and 


The  known  relation  between  the  temperature  and  the  resistance 
of  pure  platinum,  as  determined  by  the  experiments  of  Le  Chatelier, 
Callendar,  and  others,  gives  a  means  for  graduating  the  scale  for 
the  sliding  contact  to  indicate  directly  degrees  rise  in  temperature. 


INSTRUMENTS  FOR  BECORDING  EXPERIMENTAL  DATA        69 

Fig.  35  represents  a  diagram  of  the  electrical  connections  of  the 
instrument,  as  installed  in  the  laboratory.  There  are  wire  con- 
nections for  six  different  bulbs,  enabling  temperatures  to  be  read  in 
rapid  succession  for  different  parts  of  the  furnace  and  connections 
of  a  boiler  while  making  a  test.  The  switch  A  in  the  upper  left- 
hand  corner  is,  as  will  be  noted,  arranged  for  taking  readings  from 


FIG.  35. 

any  bulb.  The  sliding  resistance  wire,  above  described,  is  arranged 
in  circular  form,  corresponding  to  a  range  of  2200°  F.  for  the 
instrument.  A  galvanometer  is  seen  at  C.  B  is  a  key  for  making 
or  breaking  the  connection  from  a  battery  as  may  be  desired.  Fig. 
36  shows  the  outside  appearance  of  the  instrument. 

To  take  a  reading,  all  connections  having  been  made,  the  bulb 
is  inserted  in  the  place  the  temperature  of  which  is  to  be  measured 
and  the  index  is  moved  around  until  the  galvanometer  balances  and 
remains  stationary,  when  the  temperature  is  read  off  directly.  To 


70  EXPERIMENTAL  ENGINEERING 

test  the  instrument  for  adjustment,  the  bulb  should  be  immersed  in 
a  well-stirred  liquid  of  known  temperature  for  a  period  of  at  least 
15  minutes.  With  the  index  moved  to  the  point  on  dial  correspond- 
ing to  this  temperature,  the  galvanometer  should  balance  if  the  in- 
strument is  in  proper  adjustment.  If  not,  the  proper  correction,  as 
thus  obtained,  should  be  applied. 


FIG.  36. 

This  instrument  is  capable  of  registering  continuously  tem- 
peratures up  to  1800°  F.  By  withdrawing  the  bulb  each  time  after 
taking  a  reading,  temperatures  up  to  the  full  limit  of  the  instrument 
may  be  taken  without  injury  to  it.  It  is  very  useful  for  taking 
practically  simultaneous  temperatures  of  the  flue  gases  at  different 
points  in  a  boiler.  It  has  been  calibrated  by  comparison  with  an  air 
thermometer  and  found  to  compare  with  it  very  favorably  in  accu- 
racy. It  is  portable  and  can  be  set  up  where  needed,  while  this  can- 
not be  done  with  the  air  thermometer. 


INSTRUMENTS  FOR  RECORDING  EXPERIMENTAL  DATA        71 

Reflecting  Pyrometer. — This  instrument  is  shown  diagrammatic- 
ally  in  Fig.  37  where  the  heat  rays  from  AB  enter  the  open  end  EF 
of  a  tube  and  impinge  on  a  concave  mirror  C ,  having  one  focus  at 
EF  and  another  at  D,  where  there  is  placed  the  hot  junction  of  a 
small  thermo-couple. 

The  mirror  C  concentrates  upon  D  the  heat  image  of  the  aperture 
EF  filled  with  radiant  heat  from  the  hot  bodies  and  this  heat  image 
raises  the  temperature  of  the  thermo-couple,  giving  rise  to  an  elec- 
tro-motive force.  Connection  is  made  to  an  indicating  millivolt- 
meter  by  means  of  a  flexible  cable  and  the  indications  of  this  milli- 
voltmeter  are  calibrated  to  read  in  degrees  of  temperature  direct. 

The  relative  position  of  the  mirror  C,  the  sensitive  device  D  and 
the  aperture  EF  are  all  fixed  so  that  the  focusing  is  done  once  for 
all  and  is  never  changed  in  use. 


-^cl 


FIG.  37. — Diagram  of  the  Receiving  Tube. 

In  order  that  the  aperture  EF  may  be  entirely  filled  with  radiant 
heat  from  the  hot  body  A B  it  is  necessary  that  the  tube  be  brought 
within  a  certain  maximum  working  distance.  This  working  dis- 
tance varies  with  the  size  of  the  hot  body  and  is  measured  from  the 
apex  G  of  the  cone  GAB. 

The  rule  for  the  working  distance  is  that  the  center  ring  must  be 
within  ten  times  the  diameter  or  smallest  dimension  of  the  hot  body. 
Any  distance  less  than  this  maximum  working  distance  is  satis- 
factory and  will  not  materially  affect  the  reading.  Looking  at  the 
diagram  in  Fig.  37,  it  will  be  seen  that  if  the  hot  body  AB  were 
brought  nearer  to  G  the  only  result  would  be  that  the  outer  edges  of 
it  would  not  be  in  the  measurement  as  they  could  only  radiate  heat 
to  the  walls  of  the  tube  and  these  are  made  non-reflexing. 

The  instrument  is  calibrated  to  give  direct  temperature  reading 
without  corrections.  It  is  best  adapted  for  indicating  furnace  tem- 
peratures for  which  purpose  it  is  fairly  accurate. 


72  EXPERIMENTAL  ENGINEERING 

Revolution  Counters. — Each  main  engine  shaft  is  provided  with 
a  continuous  recording  rotary  counter  for  registering  the  number 
of  revolutions  made.  The  general  appearance  of  the  instrument  is 
shown  in  Fig.  38  and  some  of  the  details  of  the  mechanism,  from 
which  its  operation  will  be  understood,  in  Fig.  39. 


FIG.  38. 


FIG.  39. 


Maneuvering  Indicator. — On  twin  screw  ships  there  is  fitted  in 
each  engine  room  an  indicator  consisting  of  a  dial  numbered  from 
0  to  100,  with  a  red  and  a  green  hand  for  indicating  the  relative 
speed  of  the  engines.  The  green  hand  is  actuated  by  the  starboard 
engine  and  the  red  hand  by  the  port  engine.  Each  of  the  hands 
makes  one  complete  revolution  of  the  dial  for  100  revolutions  of 
the  actuating  engine. 

The  indicators  serve  as  guides  in  maneuvering.  One  engine, 
usually  the  starboard,  is  operated  at  the  required  speed  and,  if  the 
same  speed  of  revolutions  is  desired,  the  other  engine  is  regulated 
so  that  the  two  hands  move  together.  In  turbine-driven  ships, 
fitted  with  triple  screws,  the  maneuvering  indicators  are  worked 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA        73 

from  the  outboard  shafts  in  the  same  manner  as  in  twin-screw 
ships.  The  maneuvering  and  backing  turbines  are  fitted  on  the 
outboard  shafts.  The  center  turbine  does  not  come  into  action 
until  the  vessel  is  fairly  under  way,  and  in  working  the  ship  it  is 
allowed  to  run  idle. 

Multiple  Screw  Installations. — Differential  Counter  Gear.  In 
multiple  screw  installations  it  has  been  found  that  there  may  be 
considerable  variation  in  the  revolutions  made  by  the  various  shafts 
and  the  speed  will  correspond  to  the  mean  revolutions  of  all  the 
shafts.  It  therefore  becomes  important  to  have  a  device  for  regis- 
tering the  mean  number  of  revolutions.  This  is  accomplished  by 


FIG.  40. 

fitting  differential  gear  to  operate  a  counter.  In  Fig.  40  A  and  B 
are  operated  each  from  different  shafts.  A  differential  wheel  C  is 
operated  from  A  and  B  through  the  miter  wheels  D ,  E  and  F. 
The  counter  is  actuated  from  C,  the  revolutions  of  which  correspond 
to  the  mean  revolutions  of  the  two  shafts.  A  third  differential  gear 
may  be  installed  which  will  give  the  mean  of  the  readings  of  the 
other  two,  thus  enabling  us  to  obtain  directly  the  average  revolu- 
tions of  all  the  shafts  in  a  four-shaft  installation. 

A  differential  counter  has  also  been  devised  for  giving  the  mean 
revolutions  of  three  shafts,  for  use  on  triple-screw  ships. 

Tachometers. — These  instruments  are  employed  to  indicate 
directly  the  number  of  revolutions  a  shaft  is  making.  Fig.  41  illus- 
trates the  general  principle  on  which  nearly  all  such  instruments 
are  constructed.  The  shaft  a  gives  rotation  to  a  set  of  flying  balls, 
ci?  ci,  cs>  c±-  With  increased  velocity  the  balls  swing  out  around  the 
center  b,  against  the  restraining  force  of  a  spring,  and  in  so  doing 


74  EXPERIMENTAL  ENGINEERING 

pull  down  the  links  d  and  move  the  sector  h,  operating  an  index, 
which  is  mounted  on  the  axis  of  the  wheel  i.  The  index  moves  over 
a  dial  graduated  in  revolutions  per  minute.  The  wheel  i  is  a  spur 
wheel  meshing  with  a  small  pinion,  carrying  a  balance  wheel  at  gf. 


FIG.  41. 

This  prevents  fluctuation  of  the  index.     A  stop  screw  s,  permits 
adjustment  of  the  index. 

Tachometers  of  this  type  have  been  fitted  on  fast  running  shaft- 
ing of  turbine-driven  vessels,  where  they  are  very  useful  in  indi  • 
eating  the  approximate  number  of  revolutions.  They  cannot,  as  a 
rule,  be  depended  upon  to  indicate  with  exactness. 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA        75 

Portable  Tachometers. — An  instrument  of  this  type  is  shown  in 
Fig.  42.  There  is  a  set  of  change  wheels  operated  by  the  milled 
head  at  the  right  of  the  figure,,  which  serve  to  change  the  range  of 
the  instrument.  The  setting  is  indicated  automatically  by  a  movable 
plate  as  shown. 


FIG.  42. 

The  Hutchison  Marine  Tachometer. 

The  Transmitter. — Clamped  around  the  propeller  shaft  P,  Fig. 
43,  is  split  sprocket  A.  Rotation  is  imparted  to  driven  sprocket  B 
by  the  silent  chain  C.  Sprocket  B  is  loosely  mounted  on  shaft  D. 
Two  oppositely  coiled  flat  spiral  springs  E-E'  transmit  the  rotation 
of  B  to  flywheel  F  and  shaft  D,  one  end  of  each  spring  being  at- 
tached to  the  sprocket  B,  and  the  other  end  to  flywheel  F.  Any 
irregularity  of  rotation  of  B,  caused  by  variations  in  the  angular 
velocity  of  shaft  'P,  is  smoothed  out  by  E-E',  imparting  to  F  and  D 
a  constant  resultant  speed.  The  springs  are  protected  against 
breakage  from  sudden  reversal  of  P  by  the  radial  arm  G  engaging  a 
pin  H  attached  to  flywheel. 


76 


EXPERIMENTAL  ENGINEERING 


FIG.  43. 


INSTRUMENTS  FOR  BECORDING  EXPERIMENTAL  DATA        77 

On  the  inside  face  of  flywheel,  at  the  end  opposite  from  that 
occupied  by  E-Er  are  cut  gear  teeth.  These  engage  pinions  which 
actuate  the  shafts  of  magnetos  L  and  M,  supplying  alternating 
current. 

One  pinion  is  keyed  to  inductor  shaft  of  its  magneto  M. 

The  other  pinion  is  not  keyed,  but  is  so  mounted  that  when  the 
direction  of  rotation  of  main  shaft  P  is  AHEAD  the  inductor  of 
magneto  L  is  in  the  exact  rotative  relation  to  its  armature  and  pole 
shoes  as  that  of  magneto  M .  The  current  from  L  is  therefore  in 
absolute  phase  with  that  from  M.  But  when  P  is  reversed  in  rota- 
tion, the  pinion  rotates  idly  on  shaft  of  magneto  L  until  it  has 
traveled  one  hundred  and  eighty  degrees  before  rotating  same. 
This  causes  the  inductor  of  L  to  assume  an  exactly  opposite  relation 
to  its  armature  and  pole  pieces  as  obtains  at  the  same  instant  in  M, 
and  hence  the  current  from  L  is  one  hundred  and  eighty  degrees 
electrically  out  of  phase  with  M. 

We  have,  therefore,  two  wires  from  L  and  two  from  M,  running 
to  the  indicators.  At  AHEAD  these  circuits  are  in  phase.  When  P 
rotates  ASTERN,  one  is  one  hundred  and  eighty  degrees  electrically 
out  of  phase  with  the  other. 

The  Receiver. — The  indicating  instrument,  shown  in  Fig.  44,  has 
two  coils — a  moving  coil  to  which  the  pointer  is  attached,  and  a 
fixed  or  field  coil.  The  moving  coil  is  connected  electrically  to  one 
of  the  magnetos,  the  fixed  coil  to  the  other.  When  the  two  magnetos 
are  in  phase,  the  pointer  is  deflected  to  the  RIGHT,  indicating 
R.  P.  M.  AHEAD.  When  they  are  out  of  phase,  the  pointer  is  de- 
flected to  the  LEFT,  indicating  R.  P.  M.  ASTERN.  The  faster  the 
shaft  P,  Fig.  43,  turns  in  either  direction,  the  higher  the  voltage 
generated,  and  the  greater  the  deflection  of  the  pointer  calibrated  to 
conform  thereto. 

The  Hopkins  Electric  Tachometer  consists  of  a  small  direct-cur- 
rent magneto  generator  and  an  indicating  electrical  voltmeter  of 
high  grade.  The  two  parts  of  the  system  are  connected  by  a  two- 
wire  insulated  cable. 

The  principle  of  operation  of  this  apparatus  depends  on  the  fact 
that  when  a  system  of  coils  is  rotated  within  a  permanent  magnetic 
field,  a  potential  is  generated  in  direct  proportion  to  the  speed  of 
6 


78  EXPERIMENTAL  ENGINEERING 

rotation  of  the  moving  coils.  It  is  therefore  possible  to  calibrate 
the  voltmeter  in  terms  of  the  speed,  which  in  this  case  is  repre- 
sented by  revolutions  per  minute. 

Speed  recorders  working  on  the  principle  of  the  Hutchison  and 
Hopkins  instruments  have  been  proposed  many  times,  but  have  not 
been  very  successful,  due  principally  to  the  imperfect  mechanical 
details.  The  indications  at  the  voltmeter  cannot  be  true  if  there 


FIG.  44. 

is  any  variation  in  the  resistance  of  the  system.  The  Hutchison  in- 
strument overcomes  these  difficulties  in  large  measure  by  using 
alternating  current  and  thus  avoiding  the  use  of  a  commutator.  In 
the  Hopkins  instrument  it  is  claimed  that  such  difficulties  have  been 
eliminated,  by  making  the  commutator  bars  on  the  magneto  of  pure 
platinum  and  the  brushes  of  20  karat  gold.  With  this  construction 
there  are  no  oxidation  changes  or  insulating  salts  formed. 

McNab  Marine  Register  and  Indicator. — A  small  air  pump,  with 
piston  2  inches  in  diameter  and  3  inches  stroke,  designated  by  the 
inventor  as  the  Agitator,  is  connected  to  the  valve  gear,  or  other 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA       79 

moving  part  of  the  engine  capable  of  giving  a  small  reciprocating 
motion.  This  is  connected  by  half -inch  piping  with  one  or  more 
Indicators  and  Registers  in  various  locations  about  the  ship  as  may 
•  be  desired.  The  indicator  is  a  rod  connected  with  a  small  piston 
which  is  pulsated  with  each  stroke  of  the  engine.  The  register  is  a 
counter  which  is  worked  through  a  ratchet  by  the  indicator.  There 
is  a  separate  register  and  indicator  for  ahead  and  astern,  both  on 
the  same  board.  A  separate  pipe  is  provided  for  ahead  and  astern, 
with  cocks  at  the  agitator,  so  arranged  that  they  are  opened  or 
closed  automatically  when  the  engine  is  reversed. 

The  Davison  Speed  Regulator. — This  instrument  is  one  of  several 
embodying  the  same  general  principles  and  has  for  its  object  the 
keeping  of  a  certain  definite  speed  of  the  engine  when  this  is  needed 
while  steaming  in  squadron,  standardizing  over  the  measured  mile, 
etc. 

The  device  consists  essentially  of  the  following  parts :  Eef er  to 
Fig.  45  (II) ;  the  vertical  shaft  S",  carrying  a  worm  wheel  at  its 
lower  end  and  a  miter  wheel  at  its  upper  end ;  this  small  worm  wheel 
T  is  connected  by  means  of  a  worm  8'  shaft  and  bevel  gear  to  some 
part  of  the  main  engine  in  such  a  manner  that  shaft  8"  makes  one 
revolution  for  each  revolution  of  main  engine.  On  this  vessel  the 
worm  and  worm  shaft  8'  are  connected  to  the  vertical  shaft  of  the 
main  engine  counter.  The  miter  gear  on  upper  part  of  vertical  shaft 
8"  meshes  with  another  miter  gear  on  horizontal  shaft  8'"',  this 
shaft  in  turn  carries  a  hard  bronze  friction  wheel,  or  pinion  F,  and 
is  a  little  larger  in  diameter  than  the  miter  gear  on  shaft  Sf" '.  The 
position  of  friction  pinion  F  on  shaft  Sf"  is  determined  by  setting 
of  the  micrometer  screw  E  and  micrometer  wheel  0.  F  is  made  to 
revolve  with  shaft  8"'  by  means  of  a  feather  and  key.  In  the  in- 
strument, shown  in  Fig.  45,  the  micrometer  arm  E  is  graduated  by 
fives  from  forty-five  revolutions  to  one  hundred  and  twenty  revolu- 
tions, and  the  micrometer  wheel  0  is  graduated  by  tenths  from  zero 
revolution  to  five  revolutions,  so  that  the  instrument  is  capable  of 
being  set  for  revolutions  from  forty-five  to  one  hundred  and  twenty, 
by  tenths.  In  other  instruments  the  graduations  on  E  and  0  are 
arranged  to  suit  the  range  of  speed  of  the  engine  for  which  the  in- 
strument is  intended. 


80 


EXPERIMENTAL  ENGINEERING 


5 PEED 'REGULATOR, 


FIG.  45. 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA       81 

The  locking  nut  D  holds  the  setting  for  revolutions  in  permanent 
place.  There  is  an  arm  B  which  carries  on  its  inner  end  a  small 
roller  whose  object  is  to  hold  the  friction  disk  Kf  in  constant  fric- 
tional  contact  with  the  friction  pinion  F.  The  friction  disk  K  is 
supported  top  and  bottom  by  ball  bearings,  and  carries  with  it  a 
velvet-lined  pad  TL,  on  which  rests  a  timepiece.  In  this  case  the  time- 
piece is  a  large,  ordinary  commercial  stop  watch.  The  gear  con- 
nections to  the  engine,  or  moving  part  driven  from  the  engine,  are 
such  as  to  cause  the  timepiece  to  be  carried  in  a  counter-clockwise 
direction.  The  whole  mechanism  is  enclosed  in  a  brass  casing  and 
looks  very  much  like  a  small  compass  binnacle.  It  is  mounted  on 
the  floor  plate  at  the  working  platform  in  the  engine  room  so  that 
the  man  on  watch  at  the  throttle  looks  directly  down  on  the  time- 
piece and  graduated  circle  in  Fig.  45  (I). 

Eeferring  to  Fig.  45  the  circle  on  the  top  of  the  instrument,  which 
is  fixed,  as  far  as  the  mechanism  is  concerned,  is  graduated  and 
marked  from  left  and  right  of  the  central  point  in  yards,  the  scale 
of  marking  depending  on  the  number  of  yards  made  by  the  vessel 
for  each  revolution  of  the  engine.  This  distance  and  consequently 
the  whole  number  of  revolutions  corresponding  to  a  total  gain  or  loss 
of  a  particular  number  of  yards  will  vary,  depending  on  the  draft 
of  vessel,  condition  of  bottom,  state  of  sea,  etc.,  but  curves  are  fur- 
nished with  the  instrument  which  permit  corrections  to  be  easily 
applied. 

The  operation  of  the  revolution  indicator  is  as  follows :  The  time- 
piece being  wound  and  fitted  in  its  place  on  the  velvet-lined  pad 
the  hand  will  make  one  revolution  every  minute.  By  means  of  the 
micrometer  wheel  and  screw  the  instrument  is  set  for  the  revolutions 
ordered,  then,  as  long  as  the  throttle  is  manipulated  so  as  to  main- 
tain this  speed,  the  hand  of  the  watch  virtually  stands  still  and 
points  constantly  to  the  radial  arrow  shown  in  Fig.  45  (I).  If  at 
any  instant  the  engine  room  receives  word  from  the  bridge  that  the 
ship  is,  say,  forty  yards  behind  position,  the  cap  A  is  shifted  with 
reference  to  the  hand  of  the  watch,  in  the  direction  indicated  by  the 
circular  arrow,  marked  "gain,"  the  radial  arrow  would  then  be 
forty  divisions  to  the  left  of  the  hand  of  the  watch;  and  since  the 
hand  of  the  watch  moves  at  constant  and  uniform  speed  it  would  be 


82  EXPERIMENTAL  ENGINEERING 

necessary  to  impart  a  faster  counter-clockwise  motion  to  the  time- 
piece than  it  previously  had,  in  order  to  bring  the  hand  of  the  watch 
into  coincidence  with  the  radial  arrow.  Vice  versa,  if  the  ship  had 
been  ahead  of  position  by  a  given  amount  the  top  rim  would  have 
been  shifted  in  the  direction  indicated  by  the  curved  arrow,  marked 
"  lose,7'  and,  in  this  case,  the  counter-clockwise  motion  of  the  instru- 
ment would  necessarily  have  to  be  reduced  by  throttling  down  until 
the  hand  of  the  timepiece  caught  up  again  to  the  radial  arrow.  It 
is  the  work  of  only  an  instant  to  set  the  instrument  for  any  given 
speed,  and  to  lock  it  in  place  by  means  of  locknut  D,  and  the  top 
rim  A  can  also  be  shifted  instantly. 

Special  Engine  Counters. — For  taking  the  number  of  revolutions 
made  by  an  engine  during  a  short  time,  as  for  example,  on  the 
measured  mile,  it  becomes  necessary  to  adopt  a  device  for  taking 
the  exact  counter  reading  in  fractional  parts  of  a  revolution  at  the 
instant  of  making  an  observation. 

The  Taylor  Counter. — This  instrument  substitutes  for  the  usual 
numbered  wheels  in  the  ordinary  type  of  counter,  a  set  of  printing 
wheels.  By  pressing  an  electric  contact  at  the  instant  of  making  the 
observation,  a  printed  record  is  made.  This  instrument  gives  ex- 
cellent results  in  slow  moving  engines,  but  with  high  speed  turbines 
the  records  are  frequently  blurred  and  it  becomes  necessary  to  check 
with  other  instruments. 

The  Bailey  Counter. — This  consists  of  a  train  of  wheels  the  shafts 
of  which  carry  indexes  moving  over  dials.  The  wheels  in  each  pair 
are  in  the  ratio  10  to  1  and  the  instrument  when  connected  with  the 
shaft  registers  continuously  up  to  10,000,000  revolutions.  The  long 
pointer  travels  around  the  full  face  of  the  instrument- once  in  10 
revolutions  and  its  dial  is  graduated  in  tenths  of  a  revolution.  This 
pointer  and  the  two  pointers  in  the  hundreds  and  thousands  places 
have  loose  pointers  which  travel  with  them.  On  making  an  electric 
contact  at  the  instant  of  taking  the  observation  these  loose  pointers 
are  held  and  the  exact  reading  can  be  taken  with  certainty.  The 
loose  pointers  are  then  reset  ready  for  the  next  observation. 

This  counter  gives  excellent  results,  but  there  is  no  permanent 
record  and  for  careful  work  its  readings  should  be  checked  by  in- 
dependent observers. 


INSTRUMENTS  FOR  EECORDING  EXPERIMENTAL  DATA        83 

As  installed  for  trial  trips  each  of  these  special  counters  is  con- 
nected to  the  shaft  independently. 

The  Precision  Tacograph. — This  instrument,  shown  in  Fig.  46, 
is  a  recording  tachometer  and  is  employed  to  record  accurately  slight 


FIG.  46. 


fluctuations  in  the  revolutions  of  a  shaft.  A  pair  of  weights,  not 
shown  in  the  figure,  are  revolved  about  the  shaft  of  the  instrument 
and  tend  to  fly  out  against  the  force  of  restraining  springs.  Levers 
connect  the  weights  with  a  pen  under  which  the  tape  shown  in  the 
figure  is  caused  to  move  by  clockwork.  The  paper  is  perforated  at 


84  EXPERIMENTAL  ENGINEERING 

one  edge  to  suit  the  spacing  of  the  teeth  on  a  wheel  so  that  its 
movement  is  a  correct  function  of  the  time.  Lines  on  the  paper 
are  drawn  to  represent  variations  in  speed  measured  in  per  cent 
of  the  standard. 

This  instrument  makes  it  possible  to  investigate  irregularities  in 
speed  of  motors  and  machines,  and  in  the  case  of  reciprocating 
engines  permits  the  measurement  of  irregularities  in  speed  during  a 
single  revolution,  thus  enabling  us  to  investigate  directly  the  effect 
of  the  reciprocating,  parts. 

The  same  instrument  may  be  used  for  a  wide  variation  in  speed 
by  employing  a  set  of  changeable  cone  pulleys. 


CHAPTER  IV. 
MEASUREMENT  OF  THE  QUALITY  OF  STEAM. 

The  following  terms  in  thermodynamics  are  explained  in  other 
text-books,  but  as  their  meaning  must  be  clearly  understood  in  con- 
nection with  the  study  of  the  calorimetry  of  steam  they  will  be 
briefly  reviewed  here : 

Heat  as  a  term  employed  in  thermodynamics  must  be  understood 
as  that  form  of  energy  which  when  applied  produces  the  sensation 
commonly  known  as  heat. 

Quantity  of  Heat. — Heat  and  work  being  mutually  convertible, 
the  quantity  of  heat  that  passes  to  or  from  a  body  is  capable  of  defi- 
nite measurement  and  is  directly  proportionate  to  the  amount  of 
work  done  in  causing  such  heat  to  pass. 

Temperature  may  be  defined  as  heat  pressure  or  heat  intensity. 
It  is  a  measure  of  that  quality  which  when  two  bodies  are  in  contact, 
causes  heat  to  flow  from  the  one  of  higher  to  the  one  of  lower  tem- 
perature. In  steam  engineering  research  work  in  the  United  States, 
temperatures  are  usually  measured  on  the  Fahrenheit  scale,  in  which 
at  the  atmospheric  pressure  the  temperature  of  melting  ice  is 
reckoned  at  32°  and  the  temperature  of  boiling  water  at  212°. 

Absolute  Temperature  is  the  temperature  measured  from  the 
absolute  zero.  This  has  been  deduced  from  the  known  law  govern- 
ing the  relation  between  pressures,  temperatures,  and  volumes, 
which  is  PV  =  c(t  +  k),  where  P  stands  for  pressure,  V  for  vol- 
ume, t  for  temperature  as  measured  by  the  thermometer,  and  c  and 
k  are  constants.  For  the  Fahrenheit  scale  the  value  of  k  for  all 
gases  has  been  found  to  be  461°  or  493°  below  the  freezing  point  of 
water.  T,  the  absolute  temperature,  then  equals  £  +  461,  and 
PV=cT. 

Entropy  of  a  fluid  at  any  temperature  is  that  quality  by  which 
the  relation  between  temperature  and  quantity  of  heat  is  measured. 
It  is  best  understood  by  study  of  the  temperature-entropy  diagram. 
(See  page  102.) 


86  EXPERIMENTAL  ENGINEERING 

Boiling  Point  is  the  temperature  at  which  evaporation  takes  place 
and  depends  chiefly  on  the  pressure.  It  is  raised  slightly  by  the 
addition  of  foreign  matter  to  the  water,  in  solution. 

Thermal  Unit.— A  British  Thermal  Unit  (abbreviated  B.  T.  U.) 
is  the  quantity  of  heat  required  to  raise  one  pound  of  water  from 
62°  to  63°  Fah.  This  is  the  unit  adopted  by  Professor  Peabody  in 
constructing  his  tables,  on  account  of  the  ease  with  which  its  value 
may  be  verified.  The  standard  is  usually  defined  as  the  quantity 
required  to  raise  water  through  1°  from  its  freezing  point.  It  has 
not  been  practicable  to  demonstrate  this  value  experimentally. 

Specific  Heat  of  a  substance  is  the  number  of  B.  T.  U.  required 
to  raise  a  pound  of  the  substance  1°  Fah.  The  specific  heat  of  water 
is  not  quite  constant  at  varying  temperatures.  Its  value  at  32°  is 
1.0072,  decreasing  to  a  minimum  value  of  0.9948  at  about  77°,  and 
again  increasing  gradually  to  1.046  at  395°.  At  60°  and  at  104° 
its  value  is  unity.  The  specific  heat  of  saturated  steam  is  0.478. 
This  value  is  also  commonly  used  for  the  specific  heat  of  super- 
heated steam,  but  the  true  value  of  the  specific  heat  of  superheated 
steam  varies  slightly  with  the  temperature  and  pressure. 

Sensible  Heat  at  any  temperature  or  pressure  is  the  number  of 
B.  T.  U.  required  to  raise  one  pound  of  water  from  the  freezing 
point  to  the  boiling  point.  It  is  nearly  but  not  quite  equal  to 
t  —  32,  where  t  is  the  Fahrenheit  temperature  at  which  evaporation 
takes  place.  The  sensible  heat  will  be  denoted  by  S. 

Latent  Heat  is  the  number  of  B.  T.  U.  required  to  convert  one 
pound  of  water  at  any  temperature  and  pressure  into  steam  at  the 
same  pressure  and  temperature.  It  will  be  denoted  by  L. 

Total  Heat  is  the  sum  of  the  sensible  heat  and  the  latent  heat  and 
will  be  denoted  by  H. 

Joule's  Equivalent. — One  B.  T.  U.  has  been  found  by  experiment 
to  be  equivalent  to  778  foot  pounds  of  mechanical  work,  which  is 
known  as  Joule's  Equivalent. 

Saturated  Steam. — When  water  at  any  pressure  has  been  heated 
to  the  boiling  point  corresponding  to  that  pressure  and  converted 
wholly  into  steam  without  further  addition  of  heat  it  is  said  to  be 
saturated. 

Wet  Steam  is  steam  containing  a  certain  amount  of  moisture  sus- 
pended in  it. 


MEASUREMENT  OF  THE  QUALITY  OF  STEAM  87 

Superheated  Steam  is  steam  to  which  heat  has  been  added  after 
reaching  the  point  of  saturation. 

Quality  of  Steam. — In  practice  steam  is  seldom  produced  in 
the  perfectly  dry  saturated  condition,  but  contains  a  certain  amount 
of  moisture  in  the  form  of  mist,  which  is  suspended  in  it  and  carried 
along  with  it.  It  is  necessary  to  determine  the  amount  of  this  moist- 
ure during  any  steam  experiments,  though  its  complement,  the 
quality  of  the  steam  is  usually  spoken  of.  By  quality  we  mean  that 
fraction  of  the  whole  that  is  pure,  dry,  saturated  steam.  It  is  usu- 
ally denoted  by  x,  and  the  fraction  of  the  whole  that  is  moisture  or 
hot  water  merely,  is  (1  —  x).  The  percentage  of  moisture  is 

100(1-2;). 

Steam  Calorimeters. 

The  Steam  Calorimeter  is  an  instrument  for  determining  the 
amount  of  moisture  in  steam  and  from  that  the  quality.  There  are 
three  general  classes  in  common  use,  as  follows : 

(1)  Superheating  Calorimeters. 

(2)  Separating  Calorimeters. 

(3)  Condensing  Calorimeters. 

Fig.  47  shows  Prof.  Carpenter's  Throttling  Calorimeter,  which 
belongs  to  the  first  of  these  types.  It  consists  of  a  small  vessel  Af 
to  which  steam  is  supplied  through  a  stop  or  throttle  valve  and  a 
tapering  or  converging  orifice  B,  and  contains  in  its  center  a  very 
deep  cup,  into  which  a  thermometer  can  be  inserted  for  obtaining 
the  temperature  of  the  steam  in  the  calorimeter.  A  cock  C  connects 
with  a  mercury-filled  manometer  for  measuring  the  pressure  of 
steam  in  the  calorimeter.  The  exhaust  steam  is  discharged  from  the 
lower  part  of  the  calorimeter  and  may  be  permitted  to  escape  freely. 

The  principle  of  operation  follows  from  the  superheating  of  steam 
when  it  is  allowed  to  expand  freely  without  doing  work.  The  whole 
amount  of  heat  contained  in  the  steam  must  remain  constant,  but 
the  total  heat  of  vaporization  being  greater  at  a  higher  than  at  a 
lower  pressure,  the  difference  goes  to  superheat  the  steam  of  lower 
pressure. 


88  EXPERIMENTAL  ENGINEERING 

Let  p-L  —  boiler  pressure,  absolute. 

p2  —  pressure  in  calorimeter,  absolute. 
tc  —  temperature  in  calorimeter. 

LI  and  $!  =  latent  heat  and  sensible  heat  corresponding  to  plm 
H2  and  t2  =  total  heat  and  temperature  corresponding  to  p2. 
s  =  specific  heat  of  steam. 
x  =  quality  of  steam  required. 


FIG.  47. 
Then  the  heat  in  a  pound  of  steam  flowing  to  the  orifice  will  be 

and  the  heat  in  a  pound  of  steam  in  the  calorimeter  after  passing 
through  the  orifice  will  be 


Assuming  that  no  heat  is  lost  or  converted  into  work  these  two 
expressions  must  be  equal,  from  which 


MEASUREMENT  OF  THE  QUALITY  OF  STEAM  89 

Graphical  Solution  for  Throttling  Calorimeter  Determinations.  — 

In  the  practical  use  of  this  instrument  it  is  customary  to  exhaust  at 
atmospheric  pressure,  so  that  the  normal  temperature  in  the  calori- 
meter is  the  boiling  point  at  atmospheric  pressure.  H2  then  be- 
comes 1147,  from  steam  tables,  and  t2  becomes  212.  Between  the 
temperatures  at  which  the  instrument  will  be  ordinarily  used  it  will 
be  found  that  the  values  of  8l  and  L{  can  be  represented  by 

^  =  1.017^-32,  and 

^  =  1115-0.705^. 

The  expression  for  x  as  found  above,  then  becomes  by  substitution 


_  .48*c-1.017<1  /ov 

1115-0.705^ 


This  equation  may  be  written 


,  _  -  1(1.017-0.705aO  /«v 

'  0.48 

If  x  be  given  a  constant  value,  this  equation  represents  a  straight 
line  of  which  t±  and  tc  are  the  coordinates.  A  diagram  is  constructed 
by  giving  x  a  series  of  values  approaching  unity  and  drawing  the 
series  of  lines  that  will  be  represented.  This  is  shown  in  Fig.  48,  in 
which  t±  is  measured  on  the  vertical  and  tc  on  the  horizontal  axis. 
x  may  be  thus  found  graphically,  knowing  the  values  of  ^  and  tc. 

In  order  to  find  ^  it  is  necessary  to  consult  a  steam  table  and 
pick  out  the  value  corresponding  to  p^.  To  avoid  this  necessity  a 
diagram  is  constructed,  as  shown  in  Fig.  49,  where  the  ordinates 
represent  initial  absolute  pressures  instead  of  temperatures.  Simi- 
lar lines  are  drawn  to  represent  x  and  the  diagram  is  used  in  a  man- 
ner similar  to  the  preceding,  but  it  will  be  noted  that,  since  the 
pressure  does  not  vary  directly  with  the  temperature,  the  values  of 
x  are  now  represented  by  a  series  of  curves,  instead  of  straight  lines. 

Calibration  Method.  —  The  throttling  calorimeter  is  frequently 
used  to  determine  the  quality  of  steam  at  a  constant  pressure,  as  in 
boiler  tests.  In  such  cases  if  the  discharge  valve  be  closed  so  that 
the  only  outlet  is  through  the  calorimeter,  dry  saturated  steam  will 
flow  into  it.  Let  r=the  corresponding  temperature  in  the  calorim- 
eter. Equation  (1)  then  becomes 


L, 


IN  CALORIMET 
Fio.  48. 


••••••••••••••* •••••• 


I::::::::;:::::::** 


if  H-RQT  T  t!±liQ:LC;A'-JO1R!l'l^  £  FE! 


SHE 


FIG.  49. 


92 


EXPERIMENTAL  ENGINEERING 


During  the  test,  if  t  be  the  observed  temperature  in  the  calorimeter, 
the  boiler  pressure  being  the  same  as  before,  we  will  have 


and  the  percentage  of  moisture  = 

l_z-  s(y-0  _  OAS(T-t) 

Log  of  Test.— 


j  191. 


TEST  WITH  THROTTLING  CALORIMETER. 
Steam  from 


Duration 
of 

•Barom- 
eter. . 

Boiler  Pressure 

Calorimeter  Pressure 

Calorimeter 
Temp. 

Quality 
Steam 

Gage 

Abs. 

Gag-e 

Abs. 

Limitations  of  the  Throttling  Calorimeter. — If  the  percentage  of 
moisture  is  so  great  that  the  steam,  expanding  into  the  calorimeter, 
does  not  become  completely  dried,  the  instrument  is  of  no  value. 
The  theoretical  limit  is  found  for  any  initial  temperature  ^  by  put- 
ting tc  equal  to  t2  in  equations  (1)  and  (2),  pages  88  and  89.  The 
practical  limit  is  somewhat  lower  and  varies  from  2.3%  of  moisture 
at  50  pounds  boiler  pressure  to  about  1%  at  300  pounds. 

For  a  small  percentage  of  moisture,  the  throttling  calorimeter  is 
one  of  the  handiest  and  most  accurate  forms  of  apparatus. 

Professor  Thomas'  Superheating  Calorimeter. — This  instrument 
is  the  invention  of  Prof.  Carl  C.  Thomas,  of  the  University  of  Wis- 
consin. The  general  arrangement  is  shown  in  Fig.  50,  with  a  sec- 
tion through  the  calorimeter  proper  in  Fig.  51. 

Steam  is  admitted  and  after  passing  through  the  instrument, 
passes  out  to  a  condenser  or  to  the  atmosphere.  The  admission 
valve,  if  there  is  one,  is  opened  wide  to  permit  free  access  of  steam. 
A  thermometer  measures  the  temperature  of  the  steam  in  the  in- 
strument. 


MEASUREMENT  OF  THE  QUALITY  OP  STEAM 


93 


As  steam  is  passed  through  the  instrument  it  is  dried  and  then 
superheated  by  an  electric  heater  placed  within  its  walls.  The  con- 
dition of  dryness  is  indicated  by  an  immediate  rise  of  temperature, 
as  shown  by  the  thermometer,  if  more  than  the  requisite  amount  of 
electrical  energy  is  supplied. 

For  convenience  let  Et  represent  the  number  of  watts  necessary 
to  exactly  dry  the  quantity  of  steam  that  passes  through  the  instru- 


FIG.  50. 


ment.  After  noting  El  the  steam  is  superheated  by  additional  watts 
E2  up  to  a  temperature  i,  above  saturation,  of  20,  30,  100,  or  some 
other  convenient  number  of  degrees  of  superheat.  This  operation 
is  for  the  purpose  of  determining  the  rate  of  flow  or  the  weight  of 
dry  steam  Wl  passing  through  the  instrument  when  at  the  saturation 
point.  The  weight  W2  passing  through  after  superheating  will  be 
less  than  W±  by  a  percentage  which  may,  for  a  given  pressure,  be 
represented  by  a  constant  (7;  the  specific  gravity  of  superheated 
steam  being  smaller  than  that  of  saturated  steam  at  same  pressure. 
7 


EXPERIMENTAL  ENGINEERING 


FIG.  51. 


MEASUREMENT  OF  THE  QUALITY  OF  STEAM  95 

This  constant  has  been  determined  by  practical  tests  with  the  in- 
strument, as  has  also  the  number  of  watts  8  necessary  to  superheat 
a  pound  of  steam  to  t°  at  different  pressures.  The  value  8  may  be 
used  instead  of  the  specific  heat  of  steam,  and  has  the  advantage  of 
allowing  for  radiation  losses.  The  quality  of  steam  may  be  ob- 
tained, either  by  the  use  of  curves  supplied  with  the  instrument,  or 
by  calculation,  using  the  specific  heat  of  steam  at  varying  pressures. 
By  using  the  curves,  possible  errors  due  to  uncertainty  as  to  the 
value  of  the  specific  heat  are  eliminated. 

Let  W1  —  weight  of  dry  steam  passing  per  hour. 

Then,  since  one  watt  =  .0009477  B.  T.  U.  per  sec.,  or  3,412 
B.  T.  U.  per  hour,  we  have  Et  watts  ^E^x  3.412  B.  T.  IPs  per 
hour  =  the  energy  required  to  evaporate  the  water  in  Wt  pounds  of 
wet  steam. 

O    A1  O  TJI 

Let  Hx=  -^-TTT  —  —  =the  energy  thus  required,  per  pound  of 


steam,  in  B.  T.  IPs. 

Let  W2  =  CWl  =  weight  of  superheated  steam  passing  per  hour, 
then  E2  watts  =  CW18,  where  $  =  the  number  of  watts  required  to 

ET 

superheat  one  pound  of  steam  through  t°,  and  Wl=jT^-.     Substi- 
tuting this  value  of  W^  in  the  above  expression  for  Hx,  we  have 

rr    _   3.412^  X  08 
rLx—  -  ^  -   . 

^2 

Since  0  and  S  are  constants  for  any  given  pressure  and  degree  of 
superheat,  3A12CS  may  be  written  as  a  constant,  K,  and  values  of 
this  constant  are  given  for  varying  pressures  and  degrees  of  super- 
heat, by  a  set  of  curves  plotted  from  experimentally  obtained  data. 
See  Fig.  52. 

The  expression  for  Hx  then  becomes 


If  Hv  represents  the  heat  of  vaporization  of  dry  steam,  obtained 
from  the  steam  tables  for  the  pressure  indicated  by  the  original 
temperature  in  the  calorimeter,  the  quality  of  steam  passing  through 
the  calorimeter  is 

H-H 


MEASUREMENT  OF  THE  QUALITY  OF  STEAM  97 

It  is  to  be  noted  that  the  constant  K  is  independent  of  the  weight 
of  steam  flowing  through  the  calorimeter  during  superheating,  al- 
though for  clearness  consideration  of  this  weight  has  been  included 
in  the  above  explanation. 

Operation  of  the  Apparatus. — The  calorimeter  is  attached  in  a 
vertical  position  to  the  source  of  steam  supply.  This  may  be  a 
sampling  tube  of  ordinary  form,  extending  into  a  steam  pipe.  A 
special  form  of  sampling  tube  is  supplied  with  the  instrument,  de- 
signed for  use  in  collecting  samples  of  steam  in  the  various  passages 
of  a  Parsons  steam  turbine.  The  same  tube  may  be  used  for  col- 
lecting samples  of  steam  from  different  portions  of  any  steam  pas- 
sage without  disconnecting  the  instrument. 

The  box,  shown  in  Fig.  51,  is  used  as  a  water  rheostat  for  regu- 
lating the  amount  of  electrical  energy  supplied  to  the  heating  coils. 
It  is  filled  about  half  full  of  fresh  water,  to  which  one  or  two  cups- 
full  of  common  salt  are  added.  The  inverted  cone  is  lowered  or 
raised,  to  bring  more  or  less  of  its  surface  in  contact  with  the  water, 
thus  varying  the  resistance  and  permitting  a  perfect  adjustment  of 
the  amount  of  electrical  energy  supplied.  A  voltmeter  and  ammeter 
of  ordinary  form  are  fitted  between  resistance  box  and  instrument. 
Current  is  supplied  from  the  lighting  circuit  at  about  110  volts. 
About  ten  amperes  will  be  found  sufficient  for  experiments. 

Sufficient  electrical  energy  is  at  first  supplied  not  only  to  dry  the 
steam,  but  to  superheat  it  to  some  convenient  temperature.  Let  the 
watts  introduced  be  denoted  by  Et.  Raise  the  cone  of  rheostat 
slowly  until  the  thermometer  indicates  that  superheating  no  longer 
is  taking  place.  The  steam  will  then  be  at  the  point  of  saturation. 
Let  EI  denote  the  energy  then  being  supplied,  which  will  be  the 
amount  required  to  just  dry  the  steam,  and  E2,  the  watts  required 
to  superheat  through  t°=Et  —  E1. 

From  the  curves,  Fig.  52,  select  the  value  of  the  coefficient  K, 
corresponding  to  the  degree  to  which  the  steam  was  superheated,  and 
to  the  original  pressure  in  the  calorimeter,  then  calculate  the  value 

W 

of  H x  /rom  the  equation  Hx  =  Kx  -„- . 

Find  the  quality  of  the  steam  from  the  second  set  of  curves,  Fig. 

TT     TT 

53,  representing  the  equation  x—  —*—= — -  .     The  quality  may  of 

Hv 

course  be  calculated  from  the  equation  if  desired. 


MEASUREMENT  OF  THE  QUALITY  OF  STEAM  99 

Carpenter's  Improved  Separating  Calorimeter.  —  This  instrument, 
shown  in  Fig.  54,  contains  two  vessels,  one  inside  the  other.  The 
outer  vessel  surrounds  the  inner,  leaving  a  space  which  serves  as  a 
steam  jacket.  The  inner  vessel  is  provided  with  a  glass  water  gage 
10  and  scale  12. 

The  steam  under  test  is  admitted  through  the  pipe  6.  Striking 
the  bottom  of  a  perforated  cup  14,  it  is  deflected  nearly  180  degrees. 
The  water  is  thrown  off  and  passes  through  the  perforations  into  the 
inner  vessel  3,  where  the  amount  is  indicated  by  the  graduated  scale 
12  on  gage  glass.  The  steam  passes  across  the  top  of  perforated 
cup  and  into  outside  chamber,  from  which  it  is  discharged  through 
a  small  orifice  8,  of  known  area,  in  the  bottom  part. 

The  orifice  8  is  so  small  in  comparison  with  any  section  of  the 
steam  pipe  or  throttle  valve  that  there  is  no  sensible  reduction  in 
pressure  by  passing  through  the  calorimeter.  The  pressure  in  outer 
chamber  being  the  same  as  in  the  interior,  it  has  the  same  tempera- 
ture and  consequently  there  is  no  loss  by  radiation  from  the  interior 
surface  except  what  takes  place  from  the  exposed  surface  of  the 
gage  glass. 

It  has  been  demonstrated  that  the  flow  of  steam  through  a  small 
orifice  is  proportional  to  the  absolute  steam  pressure,  until  the  pres- 
sure against  which  the  flow  takes  place  equals  or  exceeds  0.6  of  that 
of  the  vessel  under  pressure.  A  special  form  of  steam  gage  is  placed 
on  the  outside  chamber,  the  inner  circle  of  which  shows  the  gage 
pressure  and  the  outer  circle  shows  the  number  of  pounds  of  steam 
that  will  escape  through  the  orifice  in  10  minutes  of  time. 

The  graduations  on  the  scale  12  show  the  weight  of  water  in 
pounds  and  hundredths  that  is  contained  in  the  inner  vessel.  The 
instrument  is  operated  at  a  constant  pressure  for  10  minutes  and  w, 
the  weight  of  water  collected,  is  read  off;  also  W,  the  weight  of  dry 
steam  that  escapes  through  the  orifice,  is  read  off  on  the  steam  gage. 
Then 


and  t-       ^      w 


W+w' 

An  earlier  form  of  this  calorimeter  is  similar  to  the  foregoing, 
except  that  the  escaping  dry  steam  is  condensed  and  weighed. 


100 


EXPERIMENTAL  ENGINEERING 


12  - 


Fio.  54. 


MEASUREMENT  OF  THE  QUALITY  OF  STEAM  101 

The  separating  calorimeter  is  accurate  and  applicable  in  all  cases 
where  the  steam  contains  moisture.  It  is  not  applicable  in  cases 
where  the  steam  is  superheated. 

The  Barrel  Calorimeter.  —  This  is  of  the  condensing  kind  and  is 
improvised  for  steam  tests  in  cases  where  other  more  accurate  ap- 
paratus cannot  be  obtained. 

A  heavy  barrel,  such  as  an  oil  barrel,  of  about  50  gallons'  capacity, 
is  employed.  This  is  placed  on  a  platform  scale  for  weighing.  A 
hose  is  provided  for  filling  it  with  cold  fresh  water  and  a  cock  in  the 
bottom  serves  for  draining  this  off.  A  pipe  connection  is  led  directly 
over  the  barrel  to  bring  the  steam  that  is  to  be  tested.  This  ends  in 
a  short  piece  of  rubber  hose  leading  straight  down  into  and  nearly 
to  the  bottom  of  the  barrel.  A  stop  valve  is  placed  just  over  the 
barrel,  with  which  to  turn  on  or  shut  off  the  steam. 

The  barrel  is  weighed  empty,  then  filled  about  three-fourths  full 
of  cold  water,  again  weighed,  and  the  temperature  of  the  water 
taken.  The  hose  is  removed  and  steam  is  blown  through  to  heat  it. 
Steam  is  then  shut  off,  and  the  hose  inserted  in  the  water,  after 
which  steam  is  blown  in  and  the  water  carefully  stirred  until  the 
temperature  rises  to  about  110°  Fah.  The  weight  is  again  taken  to 
determine  the  weight  of  steam  blown  in.  The  pressure  of  steam  is 
noted  from  the  gage  and  the  corresponding  values  of  8  and  L  taken 
from  the  steam  tables.  Then  if  W  be  the  weight  in  pounds  of  cold 
water  in  barrel  at  temperature  t19  and  w  pounds  of  wet  steam  of 
quality  x  be  blown  in,  bringing  the  weight  of  water  up  to  W  +  w 
at  temperature  £2,  and  if  no  heat  is  lost  during  the  operation,  we 
will  have,  reckoning  from  the  freezing  point, 

Heat  contained  in  cold  water  =  W(tl  —  32). 

Heat  added  in  w  pounds  of  wet  steam  =  w(xL  +  S),  and 

Heat  contained  in  water  after  blowing  in  steam 

=  (W+w)(t2-32). 
From  which 


This  method  will  not  give  the  exact  value  of  x,  since  it  is  im- 
possible to  prevent  losses  by  radiation,  and  for  accuracy  a  correc- 
tion must  be  applied  for  the  heat  equivalent  of  the  barrel.  In  prac- 


102  EXPERIMENTAL  ENGINEERING 

tice  this  is  difficult  of  determination  and  the  usual  method  is  to  neg- 
lect it,  but  to  allow  for  radiation  approximately  by  first  filling  the 
barrel  and  heating  the  water  to  about  20°  Fah.,  above  the  final  tem- 
perature t2  of  the  experiment.  This  water  is  drained  off  and  the 
barrel  immediately  refilled  for  the  purpose  of  the  experiment. 

Care  in  Selecting  Sample  of  Steam. — With  any  calorimeter,  care 
should  be  taken  in  so  placing  it  that  a  fair  sample  of  the  steam 
is  taken.  Experiments  have  proven  that  steam  taken  from  the  cen- 
ter of  a  large  pipe  contains  less  moisture  than  if  taken  near  the 
walls.  For  throttling  calorimeters,  the  American  Society  of  Me- 
chanical Engineers  recommend  that  the  calorimeter  pipe  be  ^  inch 
in  size,  that  it  extend  into  the  steam  pipe  to  within  J  inch  of  the 
opposite  wall,  that  the  inner  end  be  plugged,  and  that  it  be  provided 
with  not  less  than  twenty  J-inch  holes,  distributed  along  and  around 
its  length,  no  hole  being  closer  than  ^  inch  to  the  inner  end.  To 
obtain  satisfactory  results,  the  same  care  should  be  exercised  in 
sampling  the  steam  for  test  in  any  calorimeter. 

The  Temperature-Entropy  Diagram. 

The  Temperature-Entropy  Diagram  is  used  by  engineers  for  in- 
vestigating the  work  done  and  the  losses  that  occur  in  heat  engines, 
for  which  purpose  it  is  of  great  practical  value.  In  the  indicator 
diagram  we  have  work  or  energy  shown  by  an  area,  ordinates  rep- 
resenting force,  and  abscissas  representing  distance.  In  the  tem- 
perature-entropy diagram,  an  area  represents  heat,  an  ordinate  rep- 
resents absolute  temperature,  and  abscissae  represent  entropy. 

If  a  body  takes  in,  or  rejects,  a  quantity  of  heat  dQ,  at  the  abso- 
lute temperature  T,  the  entropy  of  the  body  is  increased,  or  de- 
creased, such  increase  or  decrease  of  entropy  being  — ^-  .  Let 

entropy  be  represented  by  the  symbol  <£,  then  the  change  of  entropy 
consequent  upon  the  addition,  or  subtraction,  of  the  quantity  of  heat 
dQ,  at  the  absolute  temperature  T,  is  expressed  by 


or  with  proper  limits, 


MEASUREMENT  OF  THE  QUALITY  OF  STEAM 


103 


If  we  now  lay  off  the  values  of  cf>  as  abscissae  and  the  absolute  tem- 
peratures as  ordinates  in  a  diagram,  we  can  plot  the  condition  of  a 
body  as  defined  by  its  entropy  and  absolute  temperature.  In  Fig. 
55,  suppose  p  a  point  so  defined,  being  the  increase  of  entropy  due 


t 

T 

i 

P 

A 

D 

B 
C 

FIG.  55. 

to  the  addition  of  a  quantity  of  heat  Q,  and  T  the  absolute  tempera- 
ture at  which  it  was  added.  The  area  ABCD  —  ^>  x  T,  but  this,  from 
equation  (2)  is  equal  to  Q,  the  heat  added,  and  brings  us  at  once  to 
the  principle  of  the  temperature-entropy  diagram. 

In  dealing  with  entropy,  as  in  dealing  with  total  heat,  an  arbitrary 
point  is  chosen,  entropy  being  reckoned  from  that  point  as  a  zero, 
and  the  entropy  of  the  substance  for  every  other  state  will  have  a 
value  which  is  perfectly  definite  and  may  be  calculated.  In  reckon- 
ing entropy,  the  condition  of  water  at  32°  Fah.  is  taken  as  the  zero. 


FIG.  56. 

The  Diagram  for  Water.— In  Fig.  56,  let  OT  and  0$  be  the 
axes  for  the  measurement  of  absolute  temperatures  and  entropy. 
Let  To  be  the  absolute  temperature  corresponding  to  32°  Fah.,  then 
<£  =  0  at  this  point,  as  we  have  assumed  the  condition  of  water  at 
32°  Fah.  to  be  the  zero  of  entropy. 


104  EXPERIMENTAL  ENGINEERING 

Now  take  one  pound  of  water  at  32°  and  add  a  small  quantity 
of  heat  to  it.  Then,  with  reference  to  the  diagram,  there  are  two 
distinct  changes;  first,  the  temperature  is  raised,  and  second,  the 
entropy  is  increased.  In  Fig.  56  the  increase  in  entropy  is  repre- 
sented by  ab,  and  the  rise  in  temperature  by  Ic,  so  that  the  new  con- 
dition of  the  water  on  the  diagram  is  represented  by  the  point  c. 
Now  let  a  little  more  heat  be  added  and  the  temperature  and  entropy 
still  further  increased,  as  by  cd  and  de,  so  that  the  new  condition  is 
now  represented  by  the  point  e.  We  can  at  once  see  that  when  the 
additions  of  heat  are  infinitely  small  and  continuous,  i.  e.,  when 
heat  is  added  proportional  to  the  rise  in  temperature,  the  points 
representing  the  condition  of  the  water  at  each  instant  will,  when 
plotted  on  the  diagram,  lie  on  a  curve  aA. 

Let  B  be  a  point  on  the  curve  whose  absolute  temperature  is  T  B . 
Then  the  area  OaBC  represents  the  quantity  of  heat  supplied  be- 
tween the  limits  of  temperature  T0  and  TB,  and  if  a  is  the  heat 
supplied  for  each  degree  of  rise  in  temperature,  i.  e.,  the  mean  spe- 

(TB 

cific  heat  of  water,  then  the  area  OaBC  =  a        dT.    The  area  of 

J  To 

any  element,  as  ef,  is  Td<j>,  and  the  whole  area  OaBC  is  equal  also  to 
j  B  Td<f>,  and  we  have 

[B  dT,  or 


or  finally 

^L  1  *•   B  /  O  \ 

Since  the  point  B  may  be  any  point  on  the  curve,  and  the  tem- 
perature T}  the  temperature  at  any  such  point,  we  may  drop  the 
subscript  B  and  write  for  the  entropy  of  water  at  any  temperature 

T          '         T  (4) 


where  T  is  the  absolute  temperature  of  the  water,  and  T0  is  the 
absolute  temperature  of  the  point  taken  as  the  zero  of  entropy,  in 
this  case  the  absolute  temperature  corresponding  to  32°  Fah. 


MEASUREMENT  OF  THE  QUALITY  OF  STEAM  105 

The  Entropy  of  Steam. — Again  referring  to  Fig.  56,,  suppose  that 
at  B  the  pound  of  water  is  completely  evaporated,  and  dry  steam 
formed  having  the  same  temperature  as  the  water  from  which  it  was 
formed.  Remembering  that  if  heat  is  added  at  constant  tempera- 
ture, the  increase  in  entropy  is  proportional  to  the  quantity  of  heat 
added,  we  see  that  the 

Increase  of  entropy  from  B=    ,,     ,    .     Heat  added  m    (5) 

Absolute  temp,  at  which  added 

The  change  is  an  isothermal  one  as  the  temperature  has  not 
changed  and  the  increase  of  entropy  BB'  is  laid  off  from  B  on  the 
horizontal  line  corresponding  to  the  absolute  temperature  of  B.  The 
distance  of  B'  from  the  axis  of  OT  measures  the  value  of  the  en- 
tropy of  one  pound  of  dry  steam  at  the  absolute  temperature  T^. 
Referring  to  equation  (5)  the  heat  added  is  the  latent  heat  of  steam 
at  the  absolute  temperature  TB,  and  calling  this  LB,  we  have 

BB'=±?-.  (6) 

*  B 

Remembering  that  B  is  any  point,  we  have,  dropping  the  sub- 
scripts, for  dry  steam  at  any  absolute  temperature  T, 

*  =  .log^  +  4-  '  (7) 

where  L  is  the  latent  heat  corresponding  to  that  temperature  and 
a  is  the  mean  specific  heat  of  water  at  that  temperature.  Plotting 
the  curve  as  given  by  equation  (7)  we  get  A' a',  Fig.  56.  Comparing 
equations  (?)  and  (4),  we  see  that  the  entropy  curve  for  dry  steam 
is  formed  by  laying  off,  from  each  point  on  the  curve  for  water,  the 

value  of  -=• ,  and  since  the  latent  heat  of  steam  decreases  as  the 

temperature  rises,  the  value  of  —^  will  decrease  as  we  ascend  the 

scale  of  temperature  and  the  curves  will  approach  each  other. 

Mixture  of  Steam  and  Water. — Again  referring  to  the  condi- 
tion of  the  water  at  the  point  B,  Fig.  56,  suppose  that  only  a  frac- 
tion, x,  is  evaporated.  We  would  have  a  mixture  of  steam  and  water, 
and  the  heat  added  at  the  point  B  would  be  xL,  and  the  increase  of 
entropy  would  be  BB",  less  than  BB'.  It  will  be  readily  seen  that 
the  entropy  in  this  case  is  given  by  the  equation 


106  EXPERIMENTAL  ENGINEERING 

It  is  evident  that  this  is  the  general  equation,  for  if  we  make 
x=0,  we  get  equation  (4)  and  if  we  make  x=l,  we  get  equation 
(7) .  Any  mixture  between  the  limits  of  all  water  and  all  steam  can 
be  represented  by  (8)  by  giving  the  proper  value  to  x,  which  is  the 
dryness  fraction,  or  quality  of  the  steam. 

Isothermal  Lines  on  Diagram. — Isothermal  changes  are  made  at 
constant  temperature,  and  are  plotted  on  the  diagram  by  straight- 
lines  parallel  to  the  line  0,  from  which  absolute  temperatures  are 
measured.  Such  a  change  occurs  when  steam  at  boiler  pressure  is 
being  admitted  to  the  cylinder;  also,  when  the  exhaust  is  being 
pushed  out  at  the  pressure  corresponding  to  the  vacuum  in 
condenser. 

Adiabatic  Lines  on  Diagram. — When  no  heat  is  received  or  given 
out  during  an  operation,  it  is  called  an  adiabatic  operation.  Ex- 
pansion and  compression  occurring  in  a  cylinder  without  gain  or 
loss  of  heat  are  adiabatic  and  are  represented  on  the  diagram  by 
vertical  lines.  Drawing  a  line  on  the  diagram  to  represent  such  an 
expansion,  it  will  be  noted  that  the  temperature  falls  and  some  of 
the  steam  is  condensed,  but  the  total  quantity  of  heat  contained  has 
remained  constant. 

If  cylinder  walls  could  be  constructed  of  non-conducting  material, 
expansion  and  compression  would  in  practice  be  adiabatic.  But 
during  expansion,  as  the  temperature  falls,  heat  is  received  from  the 
cylinder  walls  and  during  compression  heat  is  given  up  to  them. 

Temperature-Entropy  Diagram  for  an  Ideal  Engine. — In  Fig.  5? 
A"B"C"D  shows  the  cycle  of  operations  in  an  ideal  engine.  The 
cycle  begins  at  A",  the  position  of  the  point  A"  corresponding  to 
the  temperature  and  entropy  of  a  pound  of  water  just  ready  to 
form  steam.  The  isothermal  A"B"  is  the  admission  line.  As  the 
steam  is  generated,  it  is  admitted  to  the  engine  and  follows  the  pis- 
ton to  the  point  of  cut-off,  represented  by  B".  It  then  expands  with- 
out gain  or  loss  of  heat,  in  other  words  adiabatically,  to  the  end  of 
the  stroke,  where  the  pressure  and  corresponding  temperature  has 
been  reduced  to  that  of  the  condenser.  This  expansion  line  is  rep- 
resented by  B"C".  On  the  return  stroke  the  steam  is  swept  com- 
pletely out  of  the  cylinder  into  the  condenser.  This  operation  is 
represented  by  the  isothermal  G"D.  The  point  D  then  represents 


MEASUREMENT  OF  THE  QUALITY  or  STEAM 


107 


the  temperature  and  entropy  of  a  pound  of  water  in  the  condenser. 
This  water  is  returned  to  the  boiler  and  there  receives  heat,  bringing 
it  back  to  the  condition  at  the  beginning  of  the  cycle.  This  part  of 
the  operation  is  represented  by  DA". 


FIG.  57. 

Temperature-Entropy  Diagram  for  a  Real  Engine.— In  the  actual 
engine  the  conditions  are  somewhat  different.  There  is  a  slight  loss 
of  pressure  and  temperature  between  boiler  and  throttle  valve,  and 
a  further  loss  between  throttle  and  engine.  The  conditions  at 
throttle  and  engine  are  represented  by  the  lines  A 'Bf  and  AB, 
respectively.  The  cycle  of  the  ideal  engine  should  therefore  actually 
begin  at  A,  instead  of  at  A". 

At  the  beginning  of  the  stroke  there  is  a  certain  mass  of  steam 
contained  in  the  clearance  volume  of  the  cylinder,  the  amount  of 
this  depending  upon  the  point  of  exhaust  closure.  The  cycle  then 
begins  with  a  mixture  of  this  steam  and  the  water  that  is  received 
from  the  boiler.  For  one  pound  of  the  mixture,  the  cycle  in  the  real 
engine  will  therefore  not  begin  at  A,  but  at  a,  a  point  representing 
the  same  temperature  as  A,  but  greater  entropy. 


108  EXPERIMENTAL  ENGINEERING 

In  the  real  engine,  the  point  of  cut-off  will  not  fall  at  B,  but  at  1), 
and  the  real  admission  line  is  ab.  The  heat  lost  by  initial  condensa- 
tion is  represented  by  the  area  between  aB,  ah,  and  the  full  length 
of  the  ordinates  through  &  and  B. 

From  &  to  &'  the  steam  in  expanding  gives  up  heat  to  the  cylinder 
walls,  and  there  is  a  corresponding  loss  of  entropy.  At  bf  the  tem- 
perature of  the  steam  has  fallen  to  the  temperature  of  the  walls  and 
in  expanding  further  to  c,  there  is  a  gain  in  entropy  due  to  the  ab- 
sorption of  heat  from  this  scource.  At  c  the  exhaust  opens  and  the 
steam  is  permitted  to  expand  into  the  condenser,  with  falling  tem- 
perature and  partial  condensation,  the  entropy  falling  to  d,  which 
represents  the  condition  at  the  end  of  the  stroke.  From  d  to  d'  the 
steam  is  being  swept  into  the  condenser  on  the  return  stroke,  this 
line  approaching  very  closely  to  an  isothermal.  The  fact  that  this 
line  does  not  coincide  with  DC  indicates  that  there  are  resistances 
between  the  engine  and  condenser,  the  temperature  being  slightly 
higher  in  the  cylinder  than  in  the  condenser. 

At  d'  the  exhaust  closes,  that  portion  of  the  steam  received  from 
the  boiler  at  the  beginning  of  the  cycle,  having  been  returned  to  the 
condenser,  and  the  weight  contained  in  the  original  clearance  vol- 
ume having  been  retained  in  the  cylinder.  This  latter,  it  will  be 
understood,  is  in  the  form  of  steam,  which  is  then  compressed,  its 
temperature  rising,  and  since  there  is  a  loss  of  heat  to  the  walls  of 
the  cylinder,  there  is  a  slight  loss  of  entropy.  That  part  of  the 
diagram  from  dr  to  a  then  represents  the  line  for  one  pound  of  a 
mixture  of  steam  and  water,  consisting  of  that  portion  which  is 
returned  to  the  condenser,  and  thence  to  the  boiler,  combined  with 
that  portion  which  remains  in  the  cylinder  as  steam  at  the  point  of 
exhaust  closure.  The  area  between  d'a  and  DA  represents  the  loss 
due  to  clearance. 

For  further  information  regarding  the  practical  use  of  the  tem- 
perature-entropy diagram,  the  student  is  referred  to  text-books  on 
that  subject.  It  is  of  particular  value  in  investigating  the  ther- 
modynamic  changes  that  occur  in  a  steam  turbine.  By  tapping  into 
the  various  passages  in  a  turbine  and  determining  the  temperature 
and  quality  of  the  steam,  it  is  possible  to  construct  the  diagram,  and 
from  it  to  obtain  all  necessary  data  concerning  the  economical 
performance. 


MEASUREMENT  OF  THE  QUALITY  OF  STEAM  109 

In  studying  the  design  of  reciprocating  engines,  the  diagram  is 
used  as  a  means  of  analyzing  indicator  diagrams,  in  order  to  dis- 
cover thermodynamic  defects  that  may  exist. 

For  further  study  of  the  subject  the  student  is  referred  to  more 
extended  works  treating  of  it  and  its  application.  The  following 
works  treating  of  it  and  its  practical  application  are  in  the  library 
of  the  Head  of  Department  of  Marine  Engineering  and  Naval  Con- 
struction:  The  Energy  Chart,  Sankey;  The  Entropy-Temperature 
Analysis  of  Steam  Engine  Efficiencies,  Reeve ;  The  Steam  Turbine, 
Thomas;  Experimental  Engineering,  Pullen;  The  Steam  Engine, 
Creighton;  Steam  Tables  and  Diagrams,  Marks  and  Davis.  The 
last-named  volume  has  diagrams  giving  the  relation  between  pres- 
sures, qualities,  total  heats,  volumes  and  entropies  of  wet,  saturated 
and  superheated  steam.  They  will  be  found  particularly  useful  in 
solving  problems  involving  wet  or  superheated  steam. 


CHAPTEE  V. 
MEASUREMENT  OF  THE  RATE  OF  FLOW  OF  WATER. 

This  subject  becomes  of  special  importance  to  the  naval  engineer 
in  testing  the  output  of  pumping  machinery,  or  in  the  calibration 
of  instruments  used  in  such  tests. 

Water  Meters. — The  best  known  type  of  water  meter  is  the 
one  in  which  the  water  flowing  through  actuates  a  train  of  wheels, 
thus  communicating  motion  to  an  index  on  a  dial  which  registers 
the  volume  of  water  that  flows  through.  Meters  of  this  type  are 
made  by  numerous  manufacturers  and  are  more  widely  used  than 
any  other  on  account  of  their  convenience.  They  are  fairly  accu- 
rate when  used  for  indicating  the  flow  of  water  under  ordinary 
conditions,  but  they  must  be  carefully  calibrated  and  the  proper 
correction  applied  to  the  readings. 

The  Worthington  Water  Meter. — This  instrument  is  of  the 
above  type.  It  may  be  simply  described  as  a  reversed  duplex  pump, 
in  which  all  the  water  passing  through  it  is  used  to  impart  motion 
to  one  or  the  other  of  the  two  pump  pistons.  The  water  is  dis- 
tributed to  the  two  pump  cylinders  by  plain  slide  valves,  each  of 
which  is  operated  by  the  movement  of  the  opposite  piston.  The 
pistons  are  connected  up  so  that  each  movement  registers  on  the 
counter,  and  the  reading  indicates  the  volume  of  water  that  has 
passed  through,  independent  of  any  clock  mechanism  such  as  is 
necessary  in  other  types  of  meters.  The  reading  is  shown  on  a 
series  of  dials,  the  first  indicating  tenths  up  to  one  cubic  foot,  the 
second  cubic  feet  up  to  ten,  the  third  tens  of  cubic  feet  up  to  one 
hundred,  etc.  The  largest  size  meter  of  this  kind  registers  up  to 
one  million  cubic  feet. 

The  Worthington  Company  has  recently  brought  out  a  second 
form  of  meter  in  which  the  casing  contains  a  turbine  motor,  which, 
while  permitting  the  water  to  flow  through  it  with  but  little  resist- 
ance, imparts  the  necessary  movement  to  the  registering  mechanism. 
The  method  of  reading  is  similar  to  that  above  described. 


MEASUREMENT  OF  THE  KATE  OF  FLOW  OF  WATER        111 


The  Keystone  Water  Meter,  as  manufactured  by  the  Pittsburg 
Meter  Company,  is  shown  in  Fig.  58.  There  is  a  flat  disc,  D,  hav- 
ing a  ball  and  socket  bearing,  B,  which  is  adapted  to  oscillate  in  a 
chamber,  in  which  each  of  the  upper  and  lower  faces,  F  and  G, 
approximates  in  shape  the  frustum  of  a  cone,  the  extreme  confining 
wall,  W,  having  a  globular  shape.  The  disc  has  a  single  slot,  pro- 
jecting radially  from  the  boss,  which  embraces  a  fixed  metallic 


w. 


FIG.  58. 

diaphragm,  II,  set  within  and  crosswise  on  one  side  of  the  chamber. 
The  disc  is  thus  prevented  from  rotating  and  an  axial  pin,  P,  mov- 
ing around  the  cone  surface,  C,  causes  the  disc  at  all  times  to  take 
an  inclined  position,  in  contact  with  the  upper  and  lower  cone 
surfaces  of  the  chamber.  As  the  water  passes  through,  the  disc 
oscillates,  dividing  the  chamber  into  a  succession  of  sub-compart- 
ments, or  measuring  spaces.  The  oscillation  gives  a  movement  to 
P  around  C,  and  thus  operates  the  adjoining  crank,  K,  and  gives 
motion  to  the  train  of  wheels  and  register  on  plate  L. 


112 


EXPERIMENTAL  ENGINEERING 


To  determine  the  rate  of  flow  with  either  of  the  meters  as  above 
described,  it  is  necessary  to  take  readings  and  divide  the  difference 
by  the  elapsed  time  between  them. 

Meters  as  regularly  constructed  do  not  work  well  when  installed 
in  piping  on  board  ship.  This  is  due  to  the  irregular  service  and 
to  the  effect  of  hot  water  in  injuring  the  mechanism  or  causing  it 
to  register  incorrectly  on  account  of  expansion  of  certain  of  the 
parts.  They  are  generally  used  for  measuring  the  quantity  of  water 
taken  on  board  from  outside  sources.  For  this  purpose  they  are 
very  suitable. 


FIG.  59. 

In  calibrating  a  meter,  the  water  should  be  at  approximately  the 
same  temperature  as  in  the  service  for  which  the  correction  is  to 
be  applied. 

The  Venturi  Meter. — This  instrument,  though  of  a  different 
type,  is,  like  the  preceding,  used  to  determine  the  volume  of  water 
flowing  through  a  pipe.  Its  theory  is  based  on  the  discovery  made 
more  than  a  hundred  years  ago  by  an  Italian  philosopher  named 
Venturi,  that  when  water  flows  through  a  contraction  in  a  pipe, 
the  pressure  is  less  in  the  contracted  section  than  in  the  larger 
section  on  either  side. 


MEASUREMENT  OF  THE  RATE  OF  FLOW  OF  WATER        113 

If  at  any  point  in  a  pipe  through  which  water  is  flowing  a  small 
pipe  connection  is  made  and  the  small  pipe  is  carried  up  vertically, 
water  will  rise  freely  in  the  small  pipe  due  to  the  pressure  in  the 
large  pipe.  Suppose  the  flow  stopped  and  let  H=ihe  height  to 
which  the  water  will  rise  under  this  condition.  Then  if  /i  =  the 
height  to  which  the  water  will  rise  when  it  is  flowing  with  velocity 
V,  the  relation  between  H,  Ji,  and  V  is  expressed  by  the  formula 

V*  =  2g(H-h). 

Fig.  59  represents  a  longitudinal  section  through  the  Venturi 
tube.  An  annular  chamber,  A,  communicates  through  a  number 
of  holes  with  the  large  section  of  the  tube,  and  a  second  similar 
chamber,  Bf  communicates  with  the  contracted  section.  These 
chambers,  A  and  E,  have  pipes,  C  and  D,  connecting  them  with  the 
gage  for  registering  the  rate  of  flow. 

Let  lii  and  Ii2  represent  the  height  in  feet  of  the  columns  of 
water  that  would  rise  freely  in  C  and  D  respectively,  assuming  that 
C  and  D  are  carried  high  enough  and  opened  to  the  atmosphere  at 
the  upper  end.  Let  a±  and  «2  =  the  areas  of  section  at  A  and  B, 
respectively,  and  v1  and  v2  the  corresponding  velocities.  Let 
H  =  ihe  height  to  which  the  water  would  rise  when  it  is  not  flow- 
ing, and  ()  =  the  volume  discharged  per  second,  then 


v,2  =  2g(H-hi)  andv22  =  2g(H 
Assuming  no  loss  of  energy  between  A  and 


,2. 

Inserting  in  this  expression  the  values  of  v±  and  v2,  in  terms  of 
Q,  a-L  and  a2)  and  solving  for  Q,  we  have 


Q  —  a1o,2 


/2g(h1-h2) 
V     a^-a,* 


This  may  be  called  the  theoretical  discharge.  Dividing  this  ex- 
pression by  «!  gives  the  velocity  v±  and  dividing  it  by  a2  gives  the 
velocity  v2.  Owing  to  frictional  resistances  to  the  flow  of  water, 


114 


EXPERIMENTAL  ENGINEERING 


there  is  an  actual  loss  of  energy  between  A  and  B,  so  that  this 
expression  must  be  multiplied  by  a  coefficient,  thus 


at'-o,' 

The  value  of  c  has  been  determined  by  experiment  to  lie  between 
0.95  and  0.99. 

Fig.  60  shows  the  recording  apparatus  on.  a 
form  of  the  Venturi  meter,  adapted  for  labor- 
atory use,  in  which  the  difference  between  hl  and 
h2  shows  directly  on  a  scale  that  may  be  gradu- 
ated to  read  directly  the  rate  of  flow.  This 
reading  may  be  in  cubic  feet  per  hour,  gallons 
per  minute,  or  as  may  be  most  convenient. 

It  should  be  noted  that  while  this  instrument 
shows  the  rate  of  flow,  it  does  not  of  itself 
record  the  quantity  of  water  that  has  been 
delivered  through  the  tube.  To  do  this  it  is 
necessary  to  combine  it  with  a  recording  mech- 
anism. In  some  forms  of  the  instrument  this 
mechanism  actuates  a  counter  in  which  the 
speed  of  movement  is  governed  by  the  rate  of 
flow.  In  other  forms  the  rate  of  flow  is  re- 
corded by  a  pen  in  a  continuous  line  on  a  paper 
that  is  moved  by  a  clock  mechanism. 

The  Venturi  meter  is  generally  used  for 
measuring  the  discharge  through  large  water 
mains.  For  this  purpose  it  is  said  to  be  more 
reliable  than  a  self-contained  meter,  where  the 
parts  are  liable  to  wear  and  thus  increase  the 
error  of  the  readings. 

Pitot 's  Tube. — The  Pitot  tube  is  a  simple 
and,  in?  its  improved  form,  reliable  instrument 
for  determining  the  velocity  of  a  current  from 
indications  of  its  pressure.  It  was  first  used  for 
this  purpose  by  Pitot  in  1730.  In  its  simplest 
form  it  consists  of  a  vertical  glass  tube  with  a 
FIG.  60.  right-angle  bend  at  the  lower  end  placed  so  that 


MEASUREMENT  OF  THE  BATE  OF  FLOW  OF  WATER         115 


its  mouth  will  point  toward  the  direction  of  flow.  The  impulse 
pressure  of  the  flowing  water  is  balanced  by  a  column  of  water 
raised  in  the  other  leg  of  the  tube  above  the  general  level  of  the 
stream.  Pitot,  for  his  use,  enlarged  the  mouth  of  the  tube  to  a 
funnel  or  bell  shape,  as  shown  in  Fig.  61.  This,  however,  causes 
the  liquid  to  rise  a  height  li,  which  is  about  1^  times  the  true  height 
or  head  due  to  the  velocity.  This  form  of  entrance  is  additionally 
objectionable  because  it  interferes  with  the  current,  and  the  velocity 
in  front  of  the  mouth  is  not  the  same  as  the  velocity  of  the  unob- 
structed stream. 


FIG.  61. — Pitot  Tube  with  Bell  Mouth. 

Fig.  62  shows  the  improved  form  of  orifice  employed  by  Darcy 
and  Bazin,  in  which  the  tube  is  drawn  out  very  small  with  the  great 
benefit  of  interfering  little  if  any  with  the  natural  velocity  of  the 
stream;  and  also  that  the  reduced  size  of  opening  tends  to  check 
oscillations  of  the  column  of  water  in  the  tube,  instead  of  encourag- 
ing them  as  is  the  case  of  a  tube  provided  with  a  bell-shaped  mouth- 
piece. In  the  drawn-out  form,  shown  in  Fig.  62,  Darcy  found  that 
when  it  was  placed  as  shown  at  P19  the  height  h  was  almost  exactly 


when  placed  as  shown  at  P2,  having  the  plane  of  the  orifice  parallel 
to  the  direction  of  flow,  the  water  rose  practically  level  with  the  sur- 
face of  the  stream;  and  when  turned  with  the  mouth  down  stream 


116 


EXPERIMENTAL  ENGINEERING 


like  P3,  the  water  sinks  to  a  depth  h1 ',  which  is  nearly  the  same 
amount  as  the  rise  in  case  it  is  headed  up  stream  like  P^.  If  7i'  be 
the  rise  in  the  column  P1  above  the  surface  of  the  water  and  h"  be 
the  depression  in  the  column  Ps  below  the  surface,  the  pressure 

head  h  will  equal  — ^ —  nearly.    This  form  of  tube  is  made  use  of 
2 

in  the  pitometer  described  on  page  119.  Ti  - 

Darcy's  Improved  Pitot  Tube. — An  objection  to  employing  a 
simple  tube  like  Eig.  62  is  the  difficulty  of  reading  the  height  h 
direct  from  the  surface  of  the  stream.  This  is  overcome  in  Darcy's 


FIG.  62. — Improved  Form  of  Tube  employed  by  Darcy  and  Bazin. 

improved  form  of  Pitot  tube,  by  means  of  which  readings  can  be 
made  above  the  surface  of  the  stream,  or  the  instrument  may  be 
entirely  removed  from  the  water  for  that  purpose. 

Fig.  63  illustrates  the  leading  features  of  the  Darcy  instrument. 
Two  Pitot  tubes,  HE  and  JG,  made  of  copper,  have  openings  at 
right  angles  to  each  other.  In  making  velocity  measurements  the 
instrument  is  so  held  that  the  opening  in  the  end  of  the  tube  HE 
is  presented  against  the  current  while  that  of  JG  is  downward. 
The  space  between  the  tubes  is  filled  with  a  solid  piece  of  wood  or 
metal  for  strengthening  the  tubes  and  holding  them  in  place.  The 
upper  ends  of  the  tubes  are  made  of  glass  mounted  on  a  wooden 
support  WWf  which  in  turn  is  supported  by  the  clamp  Q  and  the 
guide  bracket  K  which  surround  the  standard  BE.  Each  glass  tube 


MEASUREMENT  or  THE  KATE  OF  FLOW  OF  WATER        117 


C 


FIG.   63. — Darcy's   Improved  Form  of  Pitot  Tube. 


118  EXPERIMENTAL  ENGINEERING 

is  provided  with  a  vernier  C  for  reading  the  height  of  the  columns 
on  a  vertical  scale  8.  By  means  of  the  handle  A  and  hook  L  the 
instrument  can  be  raised  or  lowered  to  any  desired  depth  and  held 
at  the  desired  elevation  by  adjustment  of  the  clamp  Q,  and  when 
thus  supported  the  main  body  of  the  instrument  acting  as  a  rudder, 
swings  itself  around  the  standard  BB  to  a  position  parallel  with 
the  current  and  presents  the  opening  of  the  tube  EH  up  stream. 

Connection  of  the  copper  tubes  to  the  glass  tubes  is  made  through 
a  two-way  cock  D  which  can  be  operated  by  cords  MM.  The  glass 
tubes  are  connected  at  their  upper  ends  by  a  brass  fitting  which  is 
provided  with  a  stop  cock  P,  the  outlet  of  which  is  provided  with  a 
piece  of  flexible  tubing  N  with  a  mouthpiece.  Having  adjusted 
the  instrument  to  the  desired  depth,  with  the  cocks  D  and  P  open, 
water  then  rises  in  the  tube  EH  to  greater  or  less  extent  above  the 
surface  of  the  stream,  while  it  rises  in  the  tube  JG  to  the  same  level 
as  that  of  the  stream.  If  then  a  little  air  be  sucked  out  of  tube  N 
and  the  cock  P  closed,  water  will  rise  in  both  glass  tubes  an  amount 
equal  to  their  respective  differences  from  atmospheric  pressure  and 
will  stand  with  the  same  relative  difference  between  their  levels  as 
they  first  had  in  the  lower  part  of  the  instrument  before  any  air  was 
exhausted.  The  cock  D  is  then  closed,  preserving  the  relative  height 
of  the  columns,  and  the  difference  is  easily  read  off  with  the  instru- 
ment in  place,  or  by  removing  it  from  the  stream. 

In  using  this  instrument  for  obtaining  the  mean  velocity  of  a 
stream,  a  number  of  readings  have  to  be  taken  to  obtain  average 
velocity  at  any  point,  as  the  velocity  of  a  stream  varies  at  different 
points  of  its  cross  section.  For  determining  the  mean  velocity  of 
a  section,  the  mean  of  averages  of  different  points  of  the  cross  sec- 
tion must  be  taken.  The  mean  velocity  of  a  stream  is  quickly  found 
by  one  accustomed  to  using  the  instrument,  once  the  cross  section 
is  established.  It  is  not  well  suited  for  measuring  very  slow  ve- 
locities. A  difficulty  which  should  be  guarded  against  is  the  liability 
of  obtaining  too  small  readings  of  the  column  connected  with  the 
tube  GJ,  due  to  dirt  gathering  in  the  opening  at  G.  This  defect 
can  be  guarded  against  by  occasional  examination  of  the  instru- 
ment before  exhausting  air  by  the  tube  N.  Using  the  instrument 
in  clear  water  rarely  gives  trouble,  but  in  all  work  of  importance  it 


MEASUREMENT  OF  THE  KATE  OF  FLOW  OF  WATER        119 

should  be  calibrated  in  water  of  known  velocity  to  obtain  its  mean 
variation  of  readings  from  the  formula, 


Darcy's  instrument  is  used  for  measuring  the  rate  of  flow  in  an 
open  stream.  Its  principle,  though,  can  be  applied  in  an  instrument 
for  measuring  the  rate  of  flow  through  pipes.  This,  follows  from 
an  examination  of  Fig.  62.  All  three  of  the  tubes  there  shown  are 
subject  to  the  static  pressure  of  the  fluid  in  the  pipe.  'P^  in  addition 
is  subject  to  the  pressure  due  to  the  rate  of  flow,  while  in  P3  the 
static  pressure  is  diminished  by  approximately  a  like  amount. 

The  Pitometer.  —  This  instrument  is  extensively  used  by  water 
works  engineers  to  determine  the  rate  of  flow  through  different 
water  mains.  The  instrument  shows  the  varying  velocity  of  flow 
in  a  water  main  by  the  deflections  of  a  colored  liquid  in  a  glass  U 
tube.  Its  accuracy  depends  upon  four  things,  viz.,  first,  the  proper 
setting  of  the  instrument  in  the  main;  second,  the  use  of  the  cor- 
rect specific  gravity  of  measuring  liquid;  third,  the  removal  of  air 
from  the  connections;  fourth,  the  use  of  the  proper  decimal  or 
coefficient  belonging  to  the  pipe  where  the  pitometer  is  used,  for 
as  is  well  known,  water  runs  more  slowly  near  the  wall  of  the  pipe 
than  at  the  center;  hence  to  get  the  correct  average  velocity  from 
which  flow  is  figured,  we  must  know  what  per  cent  it  is  of  the  ob- 
served center  velocity.  This  average  velocity  always  bears  the  same 
relation  to  the  center  velocity  in  any  one  pipe  no  matter  what  the 
rate  of  flow  is,  and,  as  we  have  found,  this  varies  from  about  70 
to  90%,  according  to  the  age  of  the  pipe  or  the  roughness  of  its 
interior  surface. 

Fig.  64  shows  the  pitometer  in  its  simplest  form.  It  consists  of 
the  Rod  Meter,  containing  the  two  Pitot  tubes  with  nozzles  for  in- 
sertion in  the  pipe,  the  U  tube  for  measuring  the  difference  in  level 
and  a  street  connection,  permanently  attached  to  the  water  main  for 
inserting  the  instrument. 

The  Rod  Meter  consists  of  a  brass  "sheath"  of  flat  oval  cress 
section  containing  two  ^-inch  brass  tubes,  each  terminating  in  a 
curved  phosphor-bronze  orifice  at  the  lower  end.  At  the  upper  end 
of  each  tube  is  clamped  a  finger,  which  engages  the  notch  marked 


120 


EXPERIMENTAL  ENGINEERING 


FIG.  64. — "  Street  Connection,"  Rod  Meter  and  Manometer  in  Place. 


MEASUREMENT  OF  THE  RATE  OF  FLOW  OF  WATER        121 

"  shut "  of  a  loose  sleeve  in  such  a  way  that  when  the  tube  is  re- 
volved to  one  position  the  orifices  will  be  turned  "  in  "  ready  for 
insertion  through  the  1-inch  pipe  tap.  Turning  the  fingers  to  en- 
gage the  other  notches  marked  "  open  "  the  orifices  will  be  turned 
"  out "  in  a  line  parallel  to  the  flat  side  of  the  oval  sheath.  This 
latter  is  the  position  of  the  orifices  when  in  use,  and  care  should 
be  taken  to  see  that  the  finger  clamps  are  so  adjusted  that  when  in 
this  position  the  orifices  will  be  in  alignment. 

The  "  IT  "  Tube  is  a.  glass  tube  about  four  feet  in  length,  bent 
in  the  middle  into  U  shape  so  as  to  bring  the  two  legs  near  together. 
The  top  of  each  leg  is  connected  by  rubber  tubing  and  the  metallic 
tubes  to  the  orifices  of  the  meter.  This  U  tube  is  filled  for  about 
half  its  height  with  a  carbon  tetrachloride  mixture  of  definite 
specific  gravity.  When  the  orifices  are  brought  into  a  current  of 
water  the  velocity  causes  the  liquid  to  rise  in  one  leg  and  fall  in  the 
other.  The  vertical  distance  between  the  tops  of  the  liquid  in  the 
two  legs  constitutes  the  "  deflection  "  by  means  of  which  the  velocity 
is  known. 

Street  Connections. — In  order  to  provide  a  convenient  method  by 
which  the  meter  may  be  repeatedly  used  upon  a  water  main  laid 
beneath  a  street  pavement,  a  street  connection,  shown  in  Fig.  65, 
is  set  at  each  point,  where  observations  are  required  and  the  pave- 
ment restored.  This  street  connection  becomes  a  part  of  the  pipe 
system  and  affords  immediate  means  of  access  at  all  times. 

The  Traverse. — The  accuracy  of  pitometer  work  depends  very 
largely  on  the  traverse  and  the  determination  of  the  pipe  coefficient 
or  decimal. 

The  pitometer  measures  velocity  only  at  that  point  in  the  pipe 
at  which  the  orifices  are  placed.  If,  while  the  discharge  of  a  pipe 
is  constant,  the  orifices  of  the  pitometer  be  moved  slowly  along 
the  diameter,  it  will  be  noticed  that  the  velocities  vary  at  each  point 
— gradually  increasing  from  the  inner  surface  toward  the  center. 

To  determine  the  quantity  of  water  being  discharged,  a  traverse 
is  first  made  of  the  pipe  at  the  gaging  point,  and  from  this  traverse 
the  pipe ' coefficient  (mean  velocity  divided  by  center  velocity)  is 
obtained.  The  orifices  are  then  left  at  the  center  and  the  mean 
velocity  at  any  rate  of  flow  may  always  be  found  by  multiplying  the 
center  velocity  by  this  coefficient. 


122  EXPERIMENTAL  ENGINEERING 

A  sufficient  number  of  traverse  velocities  should  be  taken  to  locate 
definitely  a  smooth  curve.  It  may  be  found  that  the  points  are  not 
falling  on  a  single  curve.  This  is  due  to  a  varying  center  velocity. 
The  curve  should  consist  only  of  points  which  are  taken  with  the 
same  center  velocity.  This  may  be  accomplished  by  returning  the 
orifices  quickly  to  the  center  for  a  check  reading. 

In  the  practical  use  of  this  instrument  a  recording  device  is 
arranged  to  register  continuously  the  deflection  in  the  IT  tube. 


FIG.  65. — Pitometer  Street  Connection. 

Tables  are  employed  giving  the  velocity  in  feet  per  second  for  every 
possible  amount  of  deflection  of  the  liquid,  in  the  various  sizes  of 
pipe  in  which  the  instrument  is  to  be  used. 

Weirs. — This  method  is  used  to  measure  the  flow  of  water  in 
aqueducts,  ditches,  and  other  open  streams,  where  the  size  of  the 
stream,  flow  of  water,  and  other  circumstances,  permit  the  con- 
struction of  a  dam  and  weir.  For  measuring  the  flow  of  water 
discharged  from  a  pipe,  this  method  is  also  sometimes  employed, 
using  a  tank  of  the  form  described  on  page  125. 

A  weir  for  measuring  the  flow  of  water  is  a  notch  in  the  top  of 
the  vertical  side  of  a  vessel  or  reservoir,  through  which  water  flows. 


MEASUREMENT  OF  THE  BATE  OF  FLOW  OF  WATER       123 

The  notch  is  generally  rectangular,  the  lower  edge  of  the  rectangle 
being  truly  horizontal,  and  its  sides  vertical.  The  lower  edge  of 
the  rectangle  is  called  the  "  crest "  of  the  weir.  Fig.  66  shows  an 
outline  of  the  usual  form  of  weir,  in  which  the  vertical  edges  of  the 
notch  are  sufficiently  removed  from  the  sides  of  the  reservoir  or 


FIG.  66. 

feeding  canal,  so  that  the  sides  of  the  stream  may  be  fully  con- 
tracted. This  is  called  a  weir  with  end  contractions.  In  another 
form,  not  so  often  used,  the  edges  of  the  notch  are  coincident  with 
the  sides  of  the  stream. 

In  taking  accurate  observations  of  the  rate  of  discharge  by  means 
of  a  weir,  it  is  necessary  that  the  inner  edge  of  the  notch  shall  be 
a  definite  angular  corner,  so  that  the  water  in  flowing  out  may  touch 


FIG.  67. 

the  crest  only  in  a  line,  thus  ensuring  complete  contraction.  In 
precise  observations  a  thin  metal  plate  should  be  used  for  a  crest, 
as  shown  in  Fig.  67.  Where  extreme  accuracy  is  not  important,  it 
may  be  sufficient  to  have  the  crest  formed  by  a  plank  of  smooth 
hard  wood  with  its  inner  corner  cut  to  a  sharp  right  angle  and  its 


124  EXPERIMENTAL  ENGINEERING 

outer  edge  bevelled.  In  weirs  with  end  contractions,  the  vertical 
edges  should  be  made  in  the  same  manner,  while  for  those  without 
end  contractions,  the  sides  of  the  feeding  canal  should  be  smooth 
and  prolonged  a  slight  distance  beyond  the  crest.  The  distance 
from  the  crest  to  the  bottom  of  the  feeding  canal,  or  reservoir, 
should  be  at  least  three  times  the  head  of  water  on  the  crest.  For  a 
weir  with  end  contractions,  a  similar  distance  should  exist  between 
the  vertical  edges  of  the  notch  and  the  sides  of  the  feeding  canal. 
Let  Ji  =  ihe  head  of  water  on  the  crest  •  =  the  vertical  height  of  the 
plane  of  the  level  surface  taken  well  back  of  the  weir,  above  the  edge 
over  which  the  water  flows.  Let  b  =  the  breadth  of  the  crest  in  feet, 
and  Q  =  the  discharge  in  cubic  feet  per  second.  Then  theoretically, 


Practically  the  rate  of  flow  is  not  so  great  as  this.  Extensive 
experiments  were  conducted  by  Professor  Francis  in  1854,  who  de- 
duced the  following  formulas  for  determining  the  rate  of  flow  : 

For  weirs  with  full  contraction, 


For  weirs  with  one  end  contraction  suppressed, 

0  =  3.33(&-0.1/i)P. 
For  weirs  with  both  end  contractions  suppressed, 


The  value  of  Q  thus  obtained  is  sufficiently  accurate  for  ordinary 
purposes.  If  extreme  accuracy  is  desired  it  is  best  to  consult  tables 
giving  the  number  of  cubic  feet  of  water  that  will  flow  over  a  weir 
1  inch  wide  and  of  any  given  depth.  The  figure  thus  found  is 
multiplied  by  the  width  of  the  weir  in  inches. 

The  value  of  Ji  should  not  be  less  than  0.1  foot,  and  it  rarely 
exceeds  1.5  feet.  The  least  value  of  b  in  practice  is  about  0.5  foot, 
and  it  does  not  often  exceed  20  feet. 

The  Hook  Gage.  —  The  value  of  li  must  be  determined  with  pre- 
cision in  order  to  avoid  error  in  the  computed  discharge.  Obser- 
vations of  its  value  are  sometimes  made  by  setting  up  a  stake  6  feet 
or  more  behind  the  crest  of  the  weir.  The  level  of  the  water  is 
first  marked  on  the  stake  when  the  supply  is  shut  off  and  the  water 


MEASUREMENT  OF  THE  BATE  OF  FLOW  OF  WATER        125 

just  on  the  point  of  flowing  over  the  crest.  With  the  water  flowing 
the  level  is  again  marked  on  the  stake  and  the  distance  between 
marks  is  measured.  More  reliable  observations  are  taken  by  means 
of  the  hook  gage.  A  bent  hook,  with  pointed  end  upward  is  in- 
serted in  the  lower  end  of  a  rod  sliding  vertically  in  fixed  supports, 
the  amount  of  vertical  motion  being  determined  by  the  readings  of 
a  vernier.  The  vernier  can  be  set  to  read  0.000  when  the  point  of 
the  hook  is  at  the  level  of  the  water  when  it  just  reaches  the  crest 


INLET  FOR 
WATER 


FIG.  68. 

of  the  weir.  When  the  water  is  flowing  over  the  crest  the  rod  is 
raised  by  a  tangent  screw  until  the  point  of  the  hook  is  at  the  water 
level.  With  the  water  flowing,  before  the  point  pierces  the  surface, 
a  slight  ripple  or  protuberance  will  be  seen  to  rise  above  it.  The 
hook  should  then  be  carefully  lowered  until  this  ripple  is  barely 
perceptible,  when  the  point  will  be  at  the  true  water  level.  The 
scale  and  vernier  reading  then  indicates  the  value  of  li. 

Tank  for  Weir  Apparatus. — Fig.  68  shows  a  tank  for  use  in 
measuring  the  flow  of  water  from  a  pipe,  by  means  of  a  weir.    This 
9 


126 


EXPERIMENTAL  ENGINEERING 


tank  and  weir  can  often  be  constructed  for  use  in  cases  where  an 
accurate  meter  is  not  obtainable.  In  constructing  such  a  tank  it 
should  be  sufficiently  long  to  permit  the  water  to  rise  to  a  level  and 
flow  smoothly  for  a  distance  of  at  least  6  feet  to  the  weir.  The 
water  enters  at  the  end  opposite  the  weir  and  flows  under  and  over 
a  series  of  diaphragms  that  are  so  placed  as  to  remove  the  disturb- 
ing effect  of  the  stream  of  water  pouring  in. 

This  tank  and  its  operation  have  been  described  by  Professor 
Spangler  of  the  University  of  Pennsvlvania.  as  follows : 

First  level  up  with  water  in  tank  from  lower  edge  of  weir  to 
exact  point  of  hook  gage  and  mark  on  edge  of  tank.  When  run- 
ning, raise  hook  until  a  slight  hill  of  water  just  shows  over  point, 
but  point  does  not  show.  Mark  this  on  edge  of  tank  for  height  of 


FIG.  69. 


water  over  weir.  The  difference  between  these  points  is  Ji.  The 
vertical  edges  of  weir  must  be  exactly  at  right  angles  to  the  hori- 
zontal edge  and  the  horizontal  edge  exactly  level.  The  horizontal 
edge  must  be  square  at  side  within  tank,  over  which  water  flows. 
In  Fig.  69  if  the  water  flows  across  the  side  from  a  to  &,  the  edge 
b  may  be  of  any  shape,  but  a  must  be  square.  In  flowing  over  the 
edge  a  the  water  will  turn  upward  and  it  will  be  possible  to  insert 
a  finger  nail  at  &. 

The  hook  gage  used  with  this  tank  is  made  of  -J-inch  wire  in- 
serted in  the  end  of  a  wooden  batten.  The  end  of  the  wire  is  turned 
up  to  form  a  hook  and  the  batten  is  made  adjustable  to  clamp  in  a 
vertical  position  when  held  by  a  beam  lying  across  the  tank. 

The  Right-Angled  Triangular  Weir. — In  1858  Professor  James 
Thomson,  of  Queen's  College,  Belfast,  suggested  the  use  of  the 


MEASUREMENT  OF  THE  BATE  OF  FLOW  OF  WATER        127 

right-angled  triangular  notch  with  its  apex  pointing  downward,  to 
take  the  place  of  rectangular  weirs,  because  the  latter  were  not 
adapted  to  the  measurement  of  small  and  variable  quantities  of 
water.  Another  advantage  of  the  triangular  notch  given  by  Prof. 
Thomson  is,  that  the  quantity  of  water  flowing  becomes  a  function 
of  only  one  variable,  viz.,  the  head  of  water ;  while  in  the  rectangular 
notch  it  is  a  function  of  at  least  two  quantities :  the  head  and  the 
horizontal  width.  The  application  of  the  triangular  weir  at  the 
present  time  is  limited,  but  for  some  kinds  of  laboratory  testing 
and  for  measuring  small  flows  in  irrigation  work,  it  is  very  con- 
venient. 


--b-- 


FIG.  70.  —  Triangular  Notched  Weir. 

In  Fig.  70  let 

7t:=head  of  water, 

1)  =  width  of  notch  at  level  of  the  water, 

then  the  area  of  the  notch  filled  is  %bh;  but  in  a  right-angled 
triangle 

b  =  2hf 
therefore, 


Theoretically  the  velocity  of  a  body  falling  through  a  vertical 
distance  h  is, 

V2p, 

where  g  is  the  acceleration  due  to  gravity  and  the  theoretical  dis- 
charge is, 


Thus  the  discharge  is  proportional  to  h*.    This  reasoning  was  sub- 
stantiated by  more  rigorous  mathematical  development  later. 


128  EXPERIMENTAL  ENGINEERING 

Now  it  remained  to  determine  by  experiment  whether  there  was 
some  constant  which  multiplied  by  7i*  would  give  the  quantity  of 
water  discharged  for  all  values  of  \,  that  is, 

q  =  ch*. 

After  extended  trials,  with  h  varying  from  2  to  4  inches,  the  follow- 
ing expression  was  arrived  at, 


where 

q  —  cubic  feet  discharged  per  minute,  and 

h  =  head  measured  vertically  in  inches  from  the  still-water  level 
of  the  pool  down  to  the  vertex  of  the  notch. 

It  is  the  present  custom  to  measure  all  heads  of  water  in  feet, 
and  weir  discharges  are  usually  measured  in  cubic  feet  per  second, 
thus 


The  coefficient  reduced  to  give  the  result  in  these  units  will  change 
the  equation  to, 


Miner's  Inch.  —  Though  not  used  in  steam  engineering  ex- 
perimental work,  this  unit  is  much  used  in  certain  parts  of  the 
country  and  is  here  explained  for  the  information  of  the  student. 
It  is  roughly  defined  as  the  quantity  of  water  that  will  flow  from 
a  vertical  standard  orifice  1  inch  square,  when  the  head  on  the 
center  of  the  orifice  is  6J  inches.  This  gives  a  rate  of  flow  of  about 
1.5  cubic  feet  per  minute,  which  may  be  taken  as  the  mean  value 
of  the  miner's  inch.  Owing  to  the  fact  that,  when  water  is  bought 
for  mining  or  irrigation  purposes,  a  much  larger  quantity  than  one 
miner's  inch  is  required,  orifices  much  larger  than  1  square  inch 
in  area,  and  of  various  sizes  are  used  in  measuring  it.  This  leads 
to  considerable  variation  in  the  mean  value  of  the  standard  as  used 
in  various  localities.  The  actual  value  ranges  from  1.20  to  1.76 
cubic  feet  per  minute. 


CHAPTER  VI. 
MEASUREMENT  OF  THE  RATE  OF  FLOW  OF  AIR  AND  STEAM. 

Anemometer. — This  instrument  is  used  in  measuring  the  velocity 
of  a  current  of  air.  In  steam  engineering  work  it  is  sometimes  em- 
ployed in  boiler  tests  for  determining  the  approximate  quantity  of 
air  supplied  for  combustion. 


FIG.  71. 

The  usual  form  of  such  instrument  is  shown  in  Fig.  71.  It 
consists  of  a  fan  wheel  with  dial  for  registering  the  number  of 
linear  feet  of  air  that  passes  the  fan.  The  index  can  in  the  usual 
form  of  construction  be  set  to  zero  and  the  registering  mechanism 
can  be  thrown  in  or  out  of  gear  at  will. 

To  take  an  observation,  the  index  is  set  to  zero  and  the  instru- 
ment is  placed  in  the  air  current  with  the  fan  wheel  facing  the  cur- 
rent. The  disconnector  is  withdrawn  and  the  observation  com- 


130  EXPERIMENTAL  ENGINEERING 

menced.  At  the  end  of  the  period  of  observation,  touch  the  dis- 
connector and  throw  the  movement  out  of  action,  the  result  may 
then  be  read  off.  Commencing  with  the  highest  dial,  note  carefully 
what  figure  the  index  has  actually  passed,  and  add  to  this  the  figure 
last  passed  by  the  index  of  each  succeeding  dial,  ending  with  the 
large  hand.  The  reading  represents  the  number  of  linear  feet  of 
air  passed  during  the  observation.  This  multiplied  by  the  area  in 
square  feet  of  the  cross  section  of  air  passage,  will  give  the  number 
of  cubic  feet  of  air  registered. 

In  case  the  index  cannot  be  set  to  zero,  it  should  be  noted  that  the 
reading  of  the  instrument  must  be  taken  both  before  and  after  the 
observation.  The  difference  will  then  give  the  number  of  feet  of 
air  that  have  passed. 


TUB*.  /fS'r£  TH/Ct^.  TMM£/?    TUB£  £  "  JJ//W. 


FIG.  72. 

Air  measurements  obtained  through  the  use  of  the  anemometer 
cannot  be  relied  upon,  since  the  velocities  at  different  points  in  a 
cross  section  of  an  air  pipe  are  not  uniform.  If  taken  at  the  center 
of  the  pipe  a  correction  is  sometimes  applied  to  obtain  the  mean 
velocity  through  the  pipe.  This  method  is  also  inexact  since  air  is 
an  elastic  fluid  and  does  not  always  move  in  lines  parallel  to  the  axis 
of  the  pipe.  This  is  particularly  true  where  the  velocities  are  low. 

Pitot's  Tube  for  Measuring  Low  Air  Velocities.  Taylor's  Method. 
— In  a  paper  by  Naval  Constructor  D.  W.  Taylor,  U.  S.  N.,  read 
before  the  Society  of  Naval  Architects  and  Marine  Engineers  in 
1905,  the  following  method  of  measuring  the  volume  of  air  de- 
livered by  ventilating  fans  was  proposed.  This  method  is  now 
used  for  testing  ventilating  sets  and  forced  draft  fans  for  the  Navy. 

A  special  form  of  Pitot's  tube  is  used  as  shown  in  Fig.  72. 

The  impact  pressure  is  taken  on  the  tapered  end  of  this  tube  and 


MEASUREMENT  OF  BATE  OF  FLOW  OF  AIR  AND  STEAM     131 

communicated  through  the  center  tube  to  the  right  angle  branch  at 
the  opposite  end.  The  static  pressure  is  communicated  through  the 
slots  on  sides,  and  the  annular  tube  to  the  first  right  angle  branch. 

A  nest  of  nine  of  these  tubes  is  made  up  so  that  it  exactly  fits  in  a 
slot  cut  2  inches  wide  and  13  inches  long  in  the  pipe  on  which  the 
test  is  to  be  made.  The  tubes  can  be  adjusted  as  to  depth,  depend- 
ing upon  the  size  of  the  pipe  under  test.  Stops  are  placed  so  that 
when  the  tubes  are  swung  out  against  them,  the  ends  will  come  at 
a  distance  from  the  center  such  that  each  tube  represents  an  area 
equal  to  one-ninth  of  the  whole.  The  arrangement  is  that  shown  in 
Fig.  73  where  the  cross  section  is  divided  into  nine  equal  zones, 
with  one  of  the  tubes  in  each  zone. 


FIG.  73. 

It  will  be  noted  that  tubes  1,  2  and  9  are  in  a  vertical  line,  while 
tubes  3,  5  and  7  are  in  a  line  inclined  30°  to  the  left  and  tubes  4,  6 
and  8  in  a  line  inclined  30°  to  the  right,  as  shown  further  in 
Fig.  73.  The  depth  of  setting  for  each  tube  in  any  given  diameter 
of  pipe  is  taken  from  a  diagram  furnished  with  the  apparatus. 

The  Manometer. — For  measuring  the  flow  with  the  tubes  as  thus 
arranged  a  special  form  of  manometer  is  employed,  as  shown  in 
Fig.  74.  Two  inverted  cans  are  placed  in  a  trough  of  water.  Each 
of  these  cans  is  divided  into  nine  compartments,  each  having  the 
same  cross  sectional  area,  and  a  tube  passes  through  the  bottom  of 


132 


EXPERIMENTAL  ENGINEERING 


the  trough  above  the  surface  of  the  water  into  each  compartment. 
Connecting  the  nine  impact  pressure  nozzles  with  the  nine  tubes 
under  one  can  and  the  static  pressure  nozzles  with  the  tubes  under 


FIG.  74. 

the  other  can  we  have  a  direct  means  of  measuring  the  mean  dif- 
ference between  impact  and  static  pressure  over  the  whole  cross 
section  of  air  duct.  A  sliding  weight  on  a  scale  beam  enables  the 


MEASUREMENT  OF  KATE  OF  FLOW  OF  Am  AND  STEAM      133 

two  cans  to  be  balanced  and  the  pressure  read  off  in  pounds  per 
square  foot. 

Method  of  Calculating  the  Rate  of  Flow.— The  velocity  in  the 
duct  is  given  by  the  formula 


where  v  is  the  velocity  in  feet  per  second,  W  is  the  weight  per  cubic 
foot  and  (Pi  —  p2)  is  the  difference  in  pressures  shown  by  the  tubes. 

For  ordinary  work  it  is  sufficient  to  take  17=. 0807,  which  is  the 
approximate  value  for  dry  air  at  an  atmospheric  pressure  corre- 
sponding to  normal  barometer  reading  of  29.92  inches. 

For  more  exact  observations  W  is  given  by  the  formula 

w=  .080723        _       fr-0.378e 

l  +  .0020389(*  +  32)  X     29.921    ' 

where  t  is  the  temperature  in  degrees  F.,  b  is  the  barometer  read- 
ing, and  e  is  the  pressure  due  to  the  vapor  in  the  air  in  inches  of 
mercury.  Tables  and  curves  for  applying  these  corrections  have 
been  prepared  and  are  issued  in  pamphlet  form  by  the  Bureau  of 
Construction  and  Repair,  Navy  Department. 

Having  obtained  the  mean  velocity  of  the  air,  this  multiplied  by 
the  area  of  cross  section  of  the  duct  and  by  60  gives  the  number  of 
cubic  feet  discharged  per  minute,  which  is  the  result  desired. 

Use  of  a  Single  Pilot's  Tube. — A  single  Pitot's  tube  placed  in  the 
center  of  the  duct  is  sometimes  employed,  and  a  correction  applied 
to  give  the  mean  velocity,  but  with  low  velocities,  results  thus  ob- 
tained are  not  reliable.  A  single  tube  may  be  employed  where  the 
rate  of  flow  continues  during  a  considerable  period  of  time,  long 
enough  to  permit  shifting  the  position  of  .the  tube  and  thus  obtain  a 
series  of  observations,  the  mean  of  which  gives  the  mean  velocity  in 
the  pipe. 

Measuring  the  Rate  of  Flow  of  Steam. 

Where  steam  is  discharged  through  nozzles,  the  velocity  is  given 
very  closely  by  the  following  empirical  formula  which  was  proposed 
by  Lord  Napier: 

Flow  in  pounds  per  second  =  absolute  initial  pressure  X  area  in 
square  inches  •+•  70. 


134  EXPERIMENTAL  ENGINEERING 

This  rule  is  applicable  where  the  terminal  pressure  does  not  ex- 
ceed 58%  of  the  initial  pressure.  Within  these  limits  any  variation 
in  the  terminal  pressure  does  not  affect  the  rate  of  flow. 

When  compared  with  results  obtained,  by  measuring  the  water 
consumption  on  the  trials  of  the  Curtis  marine  turbines  on  the 
IT.  S.  S.  North  Dakota,  this  formula  gave  results  within  1  to  3%. 
The  results  obtained  through  measurement  may  have  been  in  error 
to  that  extent. 

Steam  Meters. 

The  direct  measure  of  the  efficiency  of  a  steam  engine  is  the 
weight  of  steam  used  by  it  in  a  given  time  to  produce  a  given  power. 
In  engine  tests  the  steam  is  usually  condensed  and  weighed,  but  the 
same  purpose  is  accomplished  much  more  easily  if  a  reliable  steam 
meter  can  be  employed. 

Steam  meters  may  be  conveniently  grouped  in  two  general  classes, 
which,  for  lack  of  more  suitable  names,  may  be  designated  as  series 
meters,  and  shunt  meters. 

The  series  meter  is  an  integral  part  of  the  piping,  the  entire  mass 
of  fluid  to  be  measured  passing  through  the  apparatus.  The  St. 
John's  and  Venturi  meters  are  examples  of  this  class.  In  the 
former  the  volume  of  fluid  passing  is  determined  by  the  rise  and  fall 
of  a  weighted  plug  valve  and  in  the  latter  the  velocity  of  flow  is 
determined  by  the  well-known  principles  of  the  Venturi  tube.  Both 
are  indicating  instruments  and  show  only  the  rate  of  flow. 

The  Sarco  Steam  Meter.  —  This  is  another  example  of  the  series 
meter.  If  steam  be  allowed  to  expand  from  a  vessel  in  which  there 
is  a  pressure  p^  through  an  orifice  into  a  lower  pressure  p2  the 
theoretical  weight  of  steam  flowing  out  per  minute  when  p.,  is 
nearly  equal  to  />±  is  given  by  the  equation 


where  W  is  the  weight  of  steam  issuing  per  minute  in  pounds;  A 
is  the  area  of  the  orifice  in  square  inches;  p^  and  p2  the  pressures 
in  pounds  per  square  inch  (absolute)  ;  and  v±  the  specific  volume  of 
the  steam  at  pressure  p^  in  cubic  feet  per  pound. 


MEASUREMENT  OF  KATE  OF  FLOW  OF  AIR  AND  STEAM     135 


This  principle  is  applied  in  the  Sarco  meter,  where  a  disc,  1  in 
Figs.  75  and  76,  ^  inch  thick,  held  in  position  by  the  bolts  sur- 
rounding it,  is  placed  between  two  flanges  at  a  point  in  the  pipe-line 
where  it  is  desired  to  measure  the  weight  of  steam  passing. 

This  disc  has  a  bore  slightly  smaller  than  that  of  the  pipe,  causing 
the  steam  to  be  throttled  to  the  extent  of  a  drop  in  pressure  of  about 
|  pound  per  square  inch,  or  less  than  would  be  visible  on  an  ordinary 
pressure  gage. 


FIG.  76. 


The  difference  in  pressure  on  the  two  sides,  which  is  the  medium 
through  which  the  Sarco  meter  determines  the  flow  of  steam,  is 
conveyed  to  the  instrument  through  copper  pipes  of  J-inch  (or 
larger)  internal  diameter,  which  connect  with  holes  drilled  in  the 
disc,  and  communicate  with  the  high  and  low  pressure  sides. 

For  vertical  pipes  the  outlets  of  these  connecting  pipes  are 
counter-sunk  (Fig.  76)  in  such  a  way  that  no  water  can  collect  in 
the  bore  which  points  upwards,  as  this  would  cause  an  unequal  head 
on  the  two  sides  of  the  meter.  The  connecting  pipes,  before  being 
led  to  the  instrument,  are  carried  along  horizontally  in  the  same 
plane  for  a  few  feet  with  the  same  object  of  preventing  a  difference 
in  head  of  water  on  the  two  sides  which  might  result  from  unequal 


136 


EXPERIMENTAL  ENGINEERING 


condensation.     The  pipes  between  the  disc  and  meter  are  always 
kept  filled  with  water. 

The  Recorder. — The  high-pressure  side  of  the  throttle  disc  is  con- 


FIG.  77. 


nected  through  a  three-way  cock  or  valve  7  (Fig.  77)  to  the  pipe  9; 
this  leads  into  a  mercury  reservoir  10,  which  in  turn  connects  to  a 
hollow  cone  12  through  the  tube  11. 

The  cone  12  is  suspended  by  means  of  springs  26,  and  has  a  con- 


MEASUREMENT  OF  RATE  OF  FLOW  OF  AIR  AND  STEAM     137 

nection  13  at  its  upper  end.  This  gives  access  to  the  low-pressure 
side  of  the  disc  through  a  special  port  and  the  tube  8.  Thus  it  will  be 
seen  that  the  higher  pressure,  acting  through  the  water  in  the  con- 
necting tubes  upon  the  mercury  in  10  will  tend  to  drive  this  out 
along  tube  11,  thus  causing  the  cone  12  to  sink.  On  the  other  hand, 
the  lower  pressure  from  the  other  side  of  the  disc  will  press  on  the 
surface  of  the  mercury  through  8  and  13,  attempting  to  force  it 
back  into  10.  The  difference  between  the  two  pressures  will  de- 
termine the  position  of  the  cone  12.  Its  movements  are  recorded  on 
a  chart  17  by  means  of  a  pen  gear  16,  operated  through  levers  14 
and  15. 

The  chart  is  driven  by  clockwork;  it  is  arranged  for  24  hours,  and- 
is  calibrated  directly  in  pounds  of  steam  per  second.  The  total  con- 
sumption over  any  period  may  be  directly  obtained  from  this  by  an 
ordinary  planimeter.  The  charts  and  throttle  disc  to  correspond  are 
varied  for  each  different  size  of  pipe,  and  arranged  so  as  to  permit 
of  the  maximum  flow  of  steam  likely  at  the  point  in  question  to  fall 
within  the  range  provided. 

Where  it  is  desired  to  have  a  record  of  the  total  flow  of  steam  over 
a  period,  an  integrator  or  totaliser  is  fitted. 

This  consists  of  a  disc  20,  driven  by  a  separate  clock  movement, 
and  a  friction  gear  18  suspended  from  the  pen  lever  15  and  moving 
up  and  down  with  it  on  the  surface  of  the  disc  20.  A  friction  wheel 
19  is  driven  by  the  disc,  and,  by  means  of  a  worm  gear,  causes  the 
pointer  22  to  move  around  dial  21.  The  speed  of  the  pointer  will 
then  depend  upon  the  position  of  19  in  respect  of  the  periphery  of 
disc  20.  The  dials  are  calibrated  in  pounds  of  steam,  and  are  read 
once  in  24  hours. 

As  accurate  results  could  only  be  obtained  with  the  instrument 
as  so  far  described  where  the  steam  pressure  is  constant,  automatic 
compensators  are  used  where  fluctuations  exceeding  5  per  cent  have 
to  be  dealt  with. 

These  regulators  consist  of  an  oil  chamber  30  which  communi- 
cates through  small  holes  with  a  piston  31.  The  piston  rod  32  is 
held  down  by  a  strong  spring  33  connecting  to  a  segment  lever  34. 

The  regulator  is  put  under  pressure  through  tube  28  (connected 
at  27)  and  controlled  by  the  valve  29.  When  piston  31  is  forced 


138 


EXPERIMENTAL  ENGINEERING 


upwards,  the  spring  33  extends,  and  this  causes  lever  34  to  swing 
downwards,  thus  shifting  the  fulcrum  of  the  pen  lever  and  so  auto- 
matically correcting  the  chart  and  integrator  readings. 

A  simple  form  of  indicating  instrument  is  constructed  on  the 
same  principle  as  the  recorders,  for  use  as  a  load  meter.  Attached 
to  the  front  of  a  steam  boiler  with  the  throttle  disc  inserted  in  the 
main  steam  pipe,  immediately  behind  the  boiler  stop  valve,  these 
little  meters  do  excellent  service  in  showing  instantly  the  slightest 
change  in  the  load,  thus  enabling  firemen  to  adapt  their  firing  and 
prevent  the  otherwise  inevitable  loss  of  pressure — usually  the  first 
indication  of  a  change. 

Shunt  Meters. — In  the  shunt  meter  only  a  portion  of  the  steam 
to  be  measured  is  diverted  through  the  apparatus,  the  velocity  of 
flow  through  the  shunt  being  an  indication  of  that  in  the  main  pipe. 
In  this  class  one  or  more  small  openings  ^  inch  or  less  in  diameter 
suffice  for  attaching  the  apparatus  to  the  pipe.  One  instrument 
suitably  calibrated  may  answer  for  any  size  of  pipe.  The  Pitot  tube 
forms  the  basic  principle  of  practically  all  meters  of  this  class. 


Trailing  Set 


FIG.  78. 

The  General  Electric  Company's  Steam  and  Air  Flow  Meters. — 

The  principle  governing  the  action  of  the  flow  meter  is  a  modifica- 
tion of  that  of  the  Pitot  tube.  A  brass  nozzle  plug,  Fig.  78,  screwed 
into  the  pipe  at  the  point  where  the  flow  is  to  be  measured,  carries 
two  sets  of  openings :  a  leading  set,  facing  the  direction  of  flow  and 
extending  diametrically  across  the  pipe;  and  a  trailing  set,  con- 
sisting of  two  openings  at  90°  and  one  at  180°  to  the  direction  of 
flow.  The  impingement  of  the  steam  against  the  leading  openings 
sets  up  in  them  a  pressure  equal  to  the  static  pressure  plus  the 
pressure  due  to  the  velocity  head,  while  the  trailing  set  is  acted  on 
by  the  static  pressure  less  that  due  to  the  velocity.  The  difference 


MEASUREMENT  OF  KATE  OF  FLOW  OF  AIR  AND  STEAM     139 

in  these  values  is  a  measure  of  the  velocity,  and  for  constant  tem- 
perature and  pressure,  gives  the  rate  of  flow.  The  pressures  exist- 
ing in  the  two  sets  of  openings  are  communicated  through  separate 
longitudinal  tubes  to  the  outer  end  of  the  plug  and  from  there  by 
J-inch  iron  pipes  to  the  meter. 

Recording  Steam  Flow  Meter. — The  Eecording  Steam  Plow 
Meter,  Fig.  79,  is  a  curve  drawing  instrument,  accurately  calibrated 
to  record  the  total  rate  of  steam  flow  in  pounds,  per  hour  in  any 
diameter  pipe  at  any  condition  of  pressure,  temperature  or  moisture. 

In  this  meter  there  are  two  cylindrical  hollow  cups  filled  to  about 
half  their  height  with  mercury  and  joined  together  at  the  bottom 
by  a  hollow  tube.  This  "  U  "  tube  is  supported  on,  and  free  to  move 
as  a  balance  about,  a  set  of  knife  edges.  The  two  pressures  obtained 
by  the  nozzle  plug  are  communicated  to  the  cups  by  flexible  steel 
tubing,  whereupon  the  difference  in  pressure  is  equalized  by  a  rising 
of  mercury  in  the  left-hand  cup  and  a  falling  in  the  right-hand 
cup.  Due  to  the  displacement  of  the  mercury,  the  beam  carrying 
the  cups  tilts  on  the  knife  edges  until  the  moment  of  the  counter 
weights  on  the  extreme  right  of  the  meter  exactly  balances  the 
moment  caused  by  the  displacement  of  the  mercury  in  the  left-hand 
cup. 

The  motion  of  the  beam  is  multiplied  by  levers  and  is  registered 
by  a  pen.  The  time  element  of  the  meter  consists  of  an  eight-day 
clock  driving  a  drum  and  feeding  paper  at  the  rate  of  1  inch  per 
hour.  Charts  are  supplied  in  sizes  to 'measure  a  flow  of  from  2000 
to  240,000  pounds  per  hour,  and  of  sufficient  length  to  last  one 
month.  The  rate  of  flow  can  be  read  at  any  instant  or  the  average 
rate  of  flow  calculated  for  a  given  time. 

Automatic  Pressure  Correction  Device. — The  meter  is  adapted  to 
any  condition  of  pipe  diameter,  pressure,  superheat  or  moisture  by 
a  hand  adjustment  of  a  correction  weight  on  a  graduated  arm.  A 
chart  supplied  with  the  meter  shows  the  correct  position  for  any 
existing  condition. 

Eeferring  again  to  Fig.  79,  if  the  pressure  in  the  steam  main 
varies  more  than  10  pounds  from  normal,  compensation  is  neces- 
sary for  the  error  thus  introduced.  An  automatic  pressure  cor- 
rection device,  consisting  of  a  hollow  spring,  similar  to  the  pressure 


140 


EXPERIMENTAL  ENGINEERING 


MEASUREMENT  or  KATE  OF  FLOW  OF  AIR  AND  STEAM     141 


TbHo/e  L  /'/)  Mozz/ef>/tf$ 


SHQ/C/IT/NG  FLOW  METE  ft 

TYfff 
f&t/re  A 

FIG.  80. 


10 


142  EXPERIMENTAL  ENGINEERING 


FIG.  81. — Indicating  flow  meter,  type   I,  form  F  for  measuring  steam 

flow. 


MEASUREMENT  or  RATE  OF  FLOW  OF  AIR  AND  STEAM     143 

spring  in  a  steam  gage,  is  connected  so  as  to  be  influenced  by  the 
static  pressure  of  the  steam  at  the  point  where  the  flow  is  being 
measured.  Any  variation  of  the  static  pressure  causes  the  spring 
to  expand  or  contract,  and  this  movement  actuates  the  small  cor- 
rection counter  weight  and  affects  the  movement  of  the  pen  in  such 
a  manner  that  the  recorded  rate  of  flow  is  correct. 

Indicating  Steam  Flow  Meters. — The  instrument  shown  in  Figs. 
80  and  81  will  meet  general  requirements  where  an  indicating  rather 
than  a  recording  instrument  is  required. 

The  meter  consists  of  an  iron  casting,  cored  out  to  form  a  "  U  " 
tube,  and  partially  filled  with  mercury.  The  difference  in  pressures, 
as  transmitted  from  the  nozzle  plug  causes  a  difference  in  the 
mercury  levels,  and  the  displacement  of  the  mercury  actuates  a 
pulley  by  means  of  a  small  float  suspended  by  a  silk  cord.  The 
pulley  moves  a  small  "  U  "  magnet  on  the  end  of  the  shaft  next  to 
the  dial  in  proportion  to  the  change  in  level  of  the  mercury  in  the 
"  U  "  tube.  The  indicating  needle  is  mounted  in  a  separate  cylin- 
drical casing.  The  pivoted  end  consists  of  a  bar  magnet,  free  to 
turn  in  the  same  plane  as  the  magnet  on  the  inside  of  the  meter. 
The  mutual  attraction  of  the  two  magnets  keeps  them  parallel;  a 
packed  joint  to  transmit  the  motion  of  the  pulley  to  the  indicating 
needle  is  thus  eliminated. 

Proper  adjustments  for  the  existing  conditions  of  pipe  diameter, 
pressure  and  temperature  are  readily  made  by  setting  the  graduated 
cylinder  which  actuates  the  rack  carrying  the  pointer.  When  these 
settings  are  made,  the  rack  is  rotated  by  hand  until  the  pointer 
coincides  with  the  indicating  needle.  The  point  on  the  calibrated 
dial  at  the  intersection  of  the  needle  and  pointer  gives  the  true  in- 
stantaneous rate  of  flow  in  pounds  per  hour  per  square  inch  pipe 
area. 

Air  Flow  Meter. — The  Indicating  Air  Flow  Meter  is  identical  in 
principle  and  method  of  operation  with  the  Indicating  Steam  Flow 
Meter,  except  that  water  is  used  in  the  "  U  "  tube  as  a  working  fluid 
and  the  chart  dial  is  calibrated  to  read  in  cubic  feet  free  air  per 
minute  at  70°  Fah.  per  square  inch  pipe  area. 


CHAPTEE  VII. 
MEASUREMENT  OF  POWER. 

Power  is  the  term  used  to  denote  how  fast  work  is  done,  or 
energy  transferred.  Technically  it  is  denned  as  the  rate  of  doing 
work  per  unit  of  time. 

Horse  Power. — Taking  the  foot  pound  as  the  unit  of  work,  the 
horse  power  has  come  to  be  recognized  as  the  unit  of  power.  One 
horse  power  is  equivalent  to  33,000  foot  pounds  of  work  done  per 
minute. 

Indicated  Horse  Power  is  the  term  used  to  denote  the  work  done 
by  the  steam  on  the  piston  of  a  steam  engine  and  takes  its  name 
from  the  indicator. 

Brake  Horse  Power  or  Shaft  Horse  Power  is  the  power  trans- 
mitted to  the  shaft  and  is  less  than  the  indicated  horse  power  by  an 
amount  equal  to  the  friction  of  the  moving  parts.  In  an  ordinary 
steam  engine  the  brake  horse  power  is  about  85%  of  the  indicated 
horse  power.  In  a  marine  steam  turbine  the  shaft  horse  power  is 
usually  assumed  to  be  92%  of  the  indicated  horse  power  that  would 
be  developed  in  a  reciprocating  engine  that  would  transmit  to  the 
shaft  the  given  shaft  horse  power. 

Metric  Horse  Power. — The  horse  power,  cheval  vapeur,  used  in 
countries  that  employ  the  metric  system,  is  75  kilogrammeters  of 
work  per  second.  This  is  approximately  equivalent  to  32548-foot 
pounds  of  work  per  minute,  or  .9863  horse  power  in  our  units. 

Efficiency  of  a  Machine. — In  any  mechanical  apparatus  the  effi- 
ciency is  equal  to  the  ratio 

Useful  work  done  by  machine 
Total  energy  received  by  machine* 

A  large  portion  of  experimental  engineering  work  is  devoted  to 
the  determination  of  this  ratio  for  different  machines  and  resolves 
itself  into  the  measurement  of  power  and  the  calibration  of  the 
instruments  employed. 


MEASUREMENT  OF  POWER  145 

The  Steam  Engine  Indicator,  used  for  determining  the  power  de- 
veloped in  the  cylinders  of  reciprocating  engines,  is  described  in 
text-books  on  the  steam  engine,  together  with  the  methods  em- 
ployed in  taking  cards  and  in  calculating  the  power  developed  and 
the  distribution  of  steam.  We  will  therefore  take  up  only  the  errors 
that  are  likely  to  be  met  with  and  their  methods  of  correction. 

These  errors  may  be  classified  as  follows: 

(1)  Errors    due    to    incorrect    calibration    of    indicator    piston 
springs.    Springs  that  are  calibrated  cold  will  show  errors  when  hot. 

(2)  Badly  fitting  pistons.     A  piston  that  will  not  fall  through 
the  cylinder  by  its  own  weight  is  too  tight  and  will  produce  errors 
due  to  friction.    The  normal  friction  of  an  indicator  piston  should 
be  so  small  that  there  will  not  be  even  the  thickness  of  a  hair  be- 
tween the  lines  obtained  from  rising  and  falling  steam  pressures 
in  the  tests  to  determine  the  hot  scale  of  the  springs.    At  the  same 
time  if  the  piston  is  loose  enough  to  leak  sufficient  steam  to  cause 
any  back  pressure,  it  cannot  indicate  correctly. 

(3)  Errors  due  to  inertia  of  piston  and  pencil  mechanism.     A 
distorted  diagram  is  produced,  due  to  vibration  of  the  pencil.    These 
errors  are  now  reduced  to  a  minimum  by  making  the  mechanism  as 
light  as  possible. 

(4)  Errors  due  to  variable  tension  on  cord.    Paper  drum  inertia. 
With  the  crosshead  of  the  engine  moving  away  from  the  indi- 
cator, the  cord  unwinds  and  moves  the  drum  against  the  action 
of  the  drum  spring.    On  the  return  stroke  the  drum  spring  moves 
the  drum,  winding  up  the  cord.    With  the  engine  standing  still  the 
tension  on  the  cord  depends  on  the  amount  of  movement  that  has 
taken  place  against  the  drum  spring,  in  other  words  on  the  position 
of  the  engine  piston.    With  the  engine  in  operation  this  tension  is 
influenced  by  the  inertia  of  the  moving  drum,  and  for  one  particular 
speed,  the  tension  in  cord  throughout  stroke  will  be  approximately 
constant.    The  drum  spring  should  be  long  so  that  the  tension  due 
to  its  compression  will  vary  as  little  as  possible  throughout  the 
stroke.     The  drum  should  be  light  to  reduce  inertia  and  the  cord 
should  be  of  such  material  as  will  stretch  as  little  as  possible,  so  as 
not  to  distort  the  indicator  card. 

(5)  Errors  due  to  incorrect  indicator  motion.     The  mechanism 


146  EXPERIMENTAL  ENGINEERING 

for  reducing  the  motion  of  the  engine  crosshead  and  imparting 
this  reduced  motion  to  the  paper  drum  should  be  so  constructed 
that  the  reduced  motion  will  be  exactly  similar  to  that  of  the  engine 
crosshead.  If  not,  the  card  will  be  distorted.  Various  forms  of 
reducing  motions  are  in  use,,  many  of  which  are  only  approximately 
correct.  Some,  for  the  sake  of  their  simplicity,  have  been  adopted 
that  are  very  incorrect.  In  engine  tests  the  indicator  motion  should 
be  analyzed  to  determine  its  accuracy  in  reproducing  on  a  reduced 
scale  the  exact  motion  of  the  engine  piston. 

Calibration  of  Indicator  Springs. — The  manufacturers  of  recent 
high-grade  indicators  now  calibrate  their  springs  hot,  so  that  the 
errors  shown  by  them  are  small  in  comparison  with  what  they 
were  before  the  importance  of  so  calibrating  them  was  understood. 
A  spring  that  registers  correctly  to  scale  at  one  temperature  will  not 
be  correct  at  a  temperature  considerably  above  or  below  it.  In  the 
ordinary  form  of  indicator,  the  spring  is  subjected  to  the  heat  of 
the  steam,  which  increases  with  the  pressure.  For  accurate  work  it 
is  necessary  to  have  a  table  of  corrections,  to  be  applied  to  the  pres- 
sures obtained  from  the  cards,  in  order  to  obtain  the  real  pressures. 
Springs  that  have  been  accurately  calibrated  will  change  after  a  cer- 
tain period  of  time,  so  that  it  will  be  found  necessary  to  recalibrate 
them. 

In  all  forms  of  indicator  spring  testing  apparatus,  the  indicator 
is  connected  to  a  reservoir  of  steam  in  which  the  pressure  may  be 
varied  at  will,  provision  being  made  for  accurately  measuring  such 
pressure.  The  earlier  form  of  such  apparatus,  which  was  developed 
by  engineer  officers  of  the  U.  S.  Navy,  measured  the  pressure  by 
means  of  a  mercury  column.  While  much  work  of  great  value  was 
done  with  this  apparatus,  it  was  unhandy,  owing  to  the  great  height 
of  the  mercury  column,  which  it  was  necessary  to  build  into  the 
wall  of  a  tall  building.  In  later  forms  of  such  apparatus,  a  scale 
beam  is  employed  to  measure  the  pressure. 

Professor  Carpenter's  Indicator  and  Gage  Testing  Apparatus. — 
This  is  shown  in  Fig.  82  and  consists  of  a  weighing  scale  mounted 
on  a  heavy  cast  iron  box  connected  to  the  steam  reservoir.  A 
cylinder  with  a  piston  of  -|  square  inch  area  is  connected  to  this 
box  in  such  a  way  that  the  piston  balances  the  beam  of  the  scale  if 
there  is  no  pressure  in  box. 


MEASUREMENT  OF  POWER  147 

The  box  is  tapped  in  different  places  for  the  connecting  of  indi- 
cators or  gages.  In  making  a  test,  steam  is  admitted  and  the  pres- 
sure weighed  by  the  scale.  The  "  friction  of  rest "  between  the  pis- 
ton and  the  cylinder  in  which  it  works  is  intended  to  be  overcome 
by  slightly  rotating  the  piston  with  the  finger,  by  means  of  the  pro- 
jections provided  for  that  purpose.  Accurate  results  can  only  be 
obtained  after  considerable  practice. 

Professor  Cooley's  Indicator  Testing  Apparatus. — This  is  shown 
in  Fig.  83  with  a  section  through  cylinder  and  connections  shown 


FIG.  82. 

separately  in  Fig.  84.  The  indicator  is  attached  to  the  indicator 
cock,  mounted  at  A,  above  a  cylinder  B,  in  which  is  a  rotating 
plunger  C.  This  plunger  is  given  a  rapid  rotary  motion  by  means 
of  a  belt  from  a  small  electric  motor,  on  the  wheel  D.  The  wheel 
D  is  mounted  by  a  ball  bearing  and  ball  and  socket  joint  on  the  step 
E,  which  is  placed  on  the  platform  of  a  specially  constructed  plat- 
form scale.  As  pressure  is  applied  in  cylinder,  the  rotation  of 
plunger,  eliminates  the  friction  of  rest  between  plunger  and  cylinder, 
so  that  the  amount  of  the  pressure  can  be  accurately  weighed  with 
the  scale  beam.  The  wheel  F  serves  to  raise  or  lower  the  cylinder 
slightly,  thus  equalizing  the  wear  on  plunger. 

The  cylinder  B  is  in  connection  with  a  manifold  under  the  table 
through  pipe  G.    H  is  a  connection  to  the  exhaust,  on  which  is  a 


148 


EXPERIMENTAL  ENGINEERING 


valve  I,  and  a  smaller  by-pass  valve  J.  Connecting  to  manifold 
under  table  are  valves  K,  admitting  steam;  Lf  admitting  air  pres- 
sure; and  M,  admitting  water  pressure.  A  fourth  connection,  not 
shown,  goes  to  an  air  pump  for  placing  the  manifold  under  a 
vacuum. 

The  grooved  cup  above  wheel  D  serves  to  catch  any  liquid  that 


FIG.  83. 


leaks  past  plunger.     Such  liquid  is  carried  off  by  the  connections 
shown,  and  by  a  rubber  tube,  clear  of  the  apparatus. 

There  are  three  beams  on  the  scale.  N  is  for  increments  of  5 
pounds.  0  is  graduated  to  measure  fractional  increments  of  5 
pounds,  and  P,  at  the  left,  measures  descending  increments,  and  is 
chiefly  used  in  calibrating  springs  at  pressures  below  the  atmosphere. 
The  counterpoise  Q  serves  to  balance  the  apparatus  when  no  pres- 
sure is  on. 


MEASUREMENT  OF  POWER 


149 


FIG.  84. 


150  EXPERIMENTAL  ENGINEERING 

Method  of  Operation. — The  indicator  spring  being  in  place  and 
all  ready  for  testing,  start  up  the  motor  causing  plunger  to  rotate 
in  cylinder.  With  all  steam  off  and  the  exhaust  valve  open  to  the 
atmosphere,  place  all  poises  at  0  and  balance  the  scale  by  means  of 
the  counterpoise  Q.  Turn  steam  on  and  get  indicator  thoroughly 
heated.  Then,  by  means  of  the  indicator  cock,  turn  off  the  steam 
and  draw  the  atmospheric  line.  This  will  be  the  data  line  from 
which  all  measurements  must  be  taken.  Open  indicator  cock,  place 
5  pounds  on  the  scale  beam,  and  by  means  of  valve  K,  regulate  the 
pressure  of  steam  so  as  to  just  a  little  more  than  balance  the  scale 
beam.  Then  by  means  of  valve  7,  and  by-pass  3 ' ,  the  scales  can  be 
balanced  perfectly. 

When  the  scales  have  been  balanced  with  the  5  pounds  on  beam, 
take  a  small  wooden  stick  and  tap  lightly  the  cylinder  of  indicator. 
At  the  same  time  pull  the  drum  cord,  holding  the  pencil  point 
against  paper.  Be  sure  that  the  scale  is  kept  in  perfect  balance 
while  this  is  being  done.  The  light  tapping  of  indicator  cylinder  is 
to  overcome  the  friction  of  rest  between  indicator  piston  and 
cylinder. 

By  increasing  the  weights  on  scale  by  such  increments  as  may  be 
desired  and  taking  the  record  on  indicator  card  in  this  manner  for 
each  increase  of  pressure,  the  complete  record  is  obtained. 

This  method  of  testing  eliminates  the  effect  of  friction  of  in- 
dicator piston  on  the  test  cards.  In  a  well  constructed,  properly 
proportioned  indicator,  this  should  be  so  small  as  to  be  negligible. 
To  determine  the  effect  of  friction,  a  test  line  is  drawn  with  the 
steam  pressure  ascending  and  another  with  it  descending,  both  with 
the  same  setting  of  the  scale.  Half  the  distance  between  these  lines 
is  the  friction. 

Method  of  Calculating  Results. — The  area  of  plunger  is  £  square 
inch.  The  pressure  per  square  inch  on  plunger,  and  therefore  on 
indicator  piston,  will  be  twice  the  weight  shown  by  scale  beams. 
Calculating  this  and  measuring  and  dividing  by  the  height  of  test 
line  above  atmospheric  line,  we  have  the  true  scale  of  the  spring. 

Testing  for  Pressures  Below  Atmosphere. — The  same  apparatus 
may  be  used  for  tests  below  atmospheric  pressure.  The  weight  of 
plunger  (7  and  attached  parts  is  such  that  even  a  perfect  vacuum  in 


MEASUREMENT  OF  POWER  151 

cylinder  B  would  not  support  it.  A  vacuum  pump  is  connected  to 
the  manifold,  with  which  the  cylinder  B  is  placed  under  a  vacuum. 
By  means  of  beam  P}  on  the  scale,  increments  of  pressure  below  the 
atmosphere,  are  removed  and  tests  made  as  before.  Beam  P  is 
graduated  to  6  pounds,  corresponding  to  12  pounds  below  the  atmos- 
phere in  cylinder.  This  is  about  as  great  a  vacuum  as  an  ordinary 
vacuum  pump  will  produce  and  the  test  is  seldom  carried  further 
in  practice. 

The  Hospitalier-Carpentier  Manograph  for  indicating  internal 
combustion  engines  and  high-speed  steam  engines  overcomes  the  in- 

ACETYLENE 
BURNER 


PRESSURE 


7W'    OF    TRIPOD    STAND 


GENERAL  APPEARANCE. 

FIG.  85. 

herent  difficulties  of  the  ordinary  piston  type  of  indicator  which  is 
not  suitable  for  very  high-speed  engines  on  account  of  the  inertia 
of  its  moving  parts.  The  springs  in  an  indicator  also  have  a  tend- 
ency to  break,  due  to  the  almost  instantaneous  combustion  pressures 
produced  in  the  cylinders  of  internal  combustion  engines. 

The  manograph  is  shown  in  Fig.  85  with  sectional  views  in  Fig. 
86.  It  substitutes  a  beam  of  light  for  the  pencil  of  the  ordinary 
indicator  and  this  beam  traces  an  indicator  card  on  a  ground  glass 
screen.  The  light  is  projected  from  an  acetylene  burner  furnished 
with  the  instrument,  reflected  by  a  mirror  which  is  pivoted  in  two 
distinct  planes  at  right  angles  to  each  other.  Movement  in  one 


152 


EXPERIMENTAL  ENGINEERING 


MEASUKEMENT  OF  POWER  153 

plane  is  obtained  from  the  crankshaft  through  a  flexible  connection 
to  the  mirror  mechanism,  thus  producing  horizontal  motion  of  the 
beam  of  light  on  the  screen.  A  pipe  connects  the  combustion  cham- 
ber of  the  cylinder  with  a  small  circular  diaphragm,  so  arranged 
that  deflections  in  the  diaphragm  caused  by  pressure  in  the  cylinder 
act  upon  the  mechanism,,  so  as  to  rotate  the  mirror  in  the  other 
plane  and  produce  vertical  movement  in  the  beam  of  light.  The 
diaphragm  corresponds  to  an  indicator  spring,  and  may  be  changed 
to  suit  any  desired  pressure.  The  card  outlined  on  the  screen  is 
correct  as  regards  pressures  in  the  cylinder,  but  it  must  be  cor- 
rected for  the  angularity  of  connecting  rod,  which  is  not  the  case 
with  the  ordinary  steam  engine  indicator. 

The  mechanism  for  moving  the  mirror  is  arranged  so  that  the 
card  may  be  brought  to  synchronism  with  the  strokes  of  any  piston. 
Pipes  leading  to  all  the  cylinders  of  a  multicylinder  engine  may  be 
used  in  succession  by  means  of  a  several-way  cock,  thus  making  it 
possible  to  indicate  the  whole  engine  with  one  instrument. 

When  desired,  the  screen  may  be  removed  and  a  plate  holder  and 
photographic  plates  substituted,  in  order  to  obtain  a  permanent 
record.  The  principle  use,  however,  is  in  connection  with  the 
screen,  since  the  observer  is  enabled  to  note  immediately  the  effect 
upon  the  card  of  various  changes  in  the  adjustment  of  the  engine 
such  as  the  time  of  ignition,  the  position  of  throttle,  the  richness  of 
mixture,  etc.  This  feature  makes  it  particularly  valuable  for  in- 
struction purposes. 

Ripper's  Mean  Pressure  Indicator. — This  instrument,  shown  in 
Fig.  87,  consists  mainly  of  a  composition  valve  box,  having  pipe 
connections  to  both  ends  of  the  engine  cylinder,  and  fitted  with 
two  dial  pressure  gages.  By  the  automatic  action  of  the  valves  in 
the  valve  box  one  of  these  gages  is  always  in  communication  with 
the  driving  or  impelling  steam  pressure  acting  on  the  piston,  while 
the  other  receives  the  back  pressure  acting  against  the  piston.  The 
gages  are  fitted  with  fine  regulation  valves,  and  these  are  throttled 
until  the  pointers  are  practically  steady.  They  will  then  indicate 
the  exact  mean  of  the  varying  pressures  they  are  subject  to,  and  the 
difference  between  the  readings  of  the  two  gages  is  the  total  mean 
effective  pressure  acting  on  the  piston. 


154 


EXPERIMENTAL  ENGINE:  RING 


The  details  of  the  instrument  are  shown  in  Fig.  88.  Connection 
is  made  to  the  cylinder  ends  by  means  of  the  pipes  A  and  B.  The 
pipe  C  is  connected  to  the  gage  showing  the  mean  forward  pressure 
and  the  pipe  D  to  the  gage  showing  the  mean  back  pressure. 


FIG.  87. 


The  constant  communication  of  the  forward  pressure  gage  with 
the  forward  pressure  side  of  the  piston  is  secured  by  means  of  the 
ball  valve  M,  which  is  pushed  forward  at  the  end  of  every  stroke  by 
the  greater  pressure  of  the  incoming  steam,  thereby  making  com- 


MEASUREMENT  OF  POWER 


155 


municatlon  between  the  forward  pressure  gage  and  the  high  pressure 
side  of  the  piston  and  closing  the  communication  to  the  other  side 
of  the  piston.  Similarly,,  the  double  beat  valve  N,  under  the  action 
of  the  steam,  makes  the  communication  between  the  back  pressure 
gage  and  the  back  pressure  side  of  the  piston.  8  and  T  are  dirt 
collecting  pockets,  which  may  be  cleared  by  removing  the  plugs  V 
and  W. 


w 


FIG.  88. 

The  taps  at  J  and  K  are  for  blowing  through  the  instrument  when 
required,  and  the  plugs  J  and  K  are  for  filling  the  gage  syphons 
with  water. 

The  mean  pressures  are  obtained  by  throttling  a  fine  adjustment 
valve  fitted  to  each  gage,  but  in  addition,  there  are  throttling  cocks 
G  and  H  fitted  on  the  instrument  for  the  purpose  of  retaining  the 
water  in  the  gage  syphon  so  as  to  keep  the  gages  cool.  It  is  found 
that  the  water  will  not  disappear  from  the  syphons  so  long  as  these 


156 


EXPERIMENTAL  ENGINEERING 


cocks  G  and  H  are  sufficiently  throttled  to  prevent  the  range  of 
pressures  in  the  syphon  from  exceeding  about  10  pounds.  By  touch- 
ing the  syphon  tubes  C  and  D  it  is  easy  to  ascertain  whether  they 
remain  charged  with  water. 

Since  the  mean  pressures  are  obtained  with  this  instrument  by 
throttling,  they  are  on  a  time  base.  They  may  be  converted  to  the 
means  on  a  distance  base,  as  given  by  the  indicator  diagram,  by 


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FIG.  89. 

adding  a  percentage  depending  upon  the  average  point  of  cut  off 
of  the  engines,  as  follows : 

Point  of  cut  off   0.3     0.4     0.5     0.6     0.7     0.8     0.9 
Add  to  m.  e.  p.    1/70  1/30  1/25  1/30  1/40  1/50  1/100 

This  correction  may  be  conveniently  applied  by  adding  the  per- 
centage to  the  total  mean  effective  pressure  referred  to  the  low 
pressure,  as  illustrated  in  Fig.  89. 

The  inventor  claims  for  this  instrument  that  it  gives  for  ordi- 
nary engines,  a  close  approximation  to  the  results  obtained  with 


MEASUREMENT  OF  POWER  157 

an  indicator.  In  engines  working  under  a  high  degree  of  compres- 
sion,, such  as  locomotives  and  compound  non-condensing  engines,  an 
error  is  introduced  owing  to  the  reversal  of  the  valves  taking  place 
too  early  in  the  stroke.  In  these  cases  he  recommends  standardizing 
the  instrument  against  an  ordinary  indicator  for  different  positions 
of  the  link,  and  using  the  corrections  thus  arrived  at, 

Ripper's  Power  Board. — This  affords  a  means  of  determining 
the  indicated  horse  power,  from  the  readings  of  the  gages  on  the 
mean  pressure  recorder,  by  simple  mechanical  manipulation,  with- 
out calculations,  and  enables  the  engineer  to  see  almost  at  a  glance, 
what  the  engines  are  doing  and  how  the  power  is  distributed  among 
the  cylinders. 

Eef erring  to  Fig.  89,  there  are  on  the  board  a  number  of  grooves, 
one  for  each  cylinder  of  the  engine.  Each  groove  has  a  marker, 
with  pointer  to  indicate  the  mean  effective  pressure  in  that  cylinder, 
and,  for  all  except  the  low  pressure  cylinder,  there  is  an  additional 
pointer  to  show  the  equivalent  mean  effective  pressure  on  the  low 
pressure  piston.  The  relative  positions  of  markers  show  at  once  the 
relative  amount  of  work  done  in  the  various  cylinders.  By  noting 
on  a  pad,  arranged  on  the  end  of  board,  the  various  mean  effective 
pressures  referred  to  low  pressure  cylinder,  adding  them,  and  cor- 
recting, the  total  mean  effective  pressure  referred  to  the  low  pres- 
sure cylinder  is  obtained. 

A  specially  constructed  horse  power  slide  rule  is  fitted  on  the 
lower  part  of  the  board.  By  setting  the  lower  slide  to  the  total  mean 
effective  pressure  referred  to  the  low  pressure  cylinder,  and  the 
upper  slide  to  the  speed  in  revolutions  per  minute,  the  horse  power 
may  be  at  once  read  off. 

Explanation  of  the  Power  Board. — The  upper  part  of  the  board 
serves  merely  to  facilitate  reduction  of  the  mean  effective  pressure 
in  all  cylinders  to  its  equivalent  referred  to  the  low  pressure  cylin- 
der. Adding  to  the  mean  pressure  in  the  low  pressure  cylinder  the 
results  thus  obtained  for  the  H.  P.  and  I.  P.  cylinders,  the  total 
mean  effective  pressure  referred  to  the  low  pressure  cylinder  is 
obtained. 

It  will  be  seen  from  inspection  of  the  lower  part  of  the  board  that 
it  is  a  special  form  of  the  duplex  slide  rule,  adopted  for  solving  the 
11 


\ 


158  EXPERIMENTAL  ENGINEERING 

equation  I.  H.   P.  =  mean  effective  pressure  x  revs,  x  const,  which 

P  X  7? 

may  be  written  in  the  form  I.  H.  P.  =  — = .     In  order  to  limit 

Ki 

the  size  of  the  instrument,  the  various  scales  are  shortened,  such 
portion  only  being  furnished  for  each  of  them  as  is  required  for 
the  particular  engine  for  which  it  is  to  be  used. 

The  lower  fixed  pointer,  corresponds  to  the  fixed  pointer  of  a 
slide  rule.  The  pointer  on  the  M.  E.  P.  scale  may  be  placed  at  a 
distance  from  its  zero  equal  to  log  Ic  so  that  with  the  M.  E.  P. 
scale  properly  set  the  horizontal  distance  between  these  two  pointers 
equals  log  P  —  log  k.  Now  setting  the  "  Revolutions  "  scale,  so  as  to 
bring  r  opposite  the  second  pointer,  it  is  obvious  that  the  horizontal 
distance  between  0  on  this  scale  and  the  fixed  pointer  represents  the 
logarithm  of  the  I.  H.  P.  In  order  to  obtain  a  direct  reading  of 
this  value,  a  third  scale  of  horse  power  is  used,  which  is  read  oppo- 
site a  pointer  on  the  revolutions  scale.  In  order  to  make  the  in- 
strument more  compact,  this  pointer  is  placed  some  distance  to 
the  right  of  the  0  on  the  revolutions  scale,  and  the  pointer  on  the 
M.  E.  P.  scale  is  found  to  the  left  of  the  true  value  of  c,  these 
changes  being  compensated  for  by  a  corresponding  shift  in  the  posi- 
tion of  the  horse  power  scale. 

Though  devised  for  use  in  connection  with  the  mean  pressure 
indicator,  this  power  board  may  be  used  with  the  ordinary  engine 
indicator  and  a  slide  rule  of  this  type  may  be  constructed  for  use 
in  calculating  horse  powers  from  brake  or  torsionmeter  readings 
of  any  particular  engine,  where  the  calculations  are  made  from  the 
general  formula 

r>X  D 

Horse  power  =  -       -. 
k 

Hudson's  Horse  Power  Scale. — This  is  a  compound  slide  rule 
for  horse  power,  similar  to  that  described  above,  but  in  place  of  the 
pointer  on  the  lower  fixed  part  of  the  instrument,  as  shown  in  Fig. 
89,  there  is  a  scale  of  cylinder  diameters,  which  makes  the  instru- 
ment adapted  to  any  engine  within  the  limits  of  its  construction. 

Another  form  of  logarithmic  scale,  adapted  to  the  computation 
of  horse  power,  which  may  be  readily  constructed  by  anyone  pro- 
vided with  the  necessary  drawing  materials,  is  shown  in  Fig.  90. 


MEASUREMENT  OF  POWER 


159 


-I7O 
'-'/SO 

-/so 

-/20 
-110 


-35OO 
-3000 
-2500 
-2000 
-/7SO 
-/fOO 
-/ZSO 


500 
400 
350 
300 
250 
ZOO 
/7S 
/39 
/Z3 
/OO 


Zf 


r 

9 


/o 


H 
FIG.  90. 


160  EXPERIMENTAL  ENGINEERING 

Writing  the  expression  for  horse  power  in  the  form 

I.  H.  P.=  P*R  ,  or  I.H.P.xfc='Pxfl. 
We  have 

log  I.  H.  P.  +  log  k= log  P  +  log  R. 

In  Fig.  90  assume  a  base  line  AB  and  erect  two  perpendicu- 
lars, AC  and  BD.  On  one  of  these,  as  AC,  construct  a  scale  to 
represent  various  values  of  log  P.  On  the  other,  construct  a  simi- 
lar scale  to  represent  various  values  of  log  R.  Assume  any  two 
values  of  P  and  R,  such  that  AE  =  log  P  and  BF=\og  R.  Draw 
EF  and  bisect  at  G.  Drop  a  perpendicular  to  the  point  H  on  AB. 
Then 

rjr_  AE+BF  _  logP+logff  _  log  I.  H.  P.  +  log  A; 
22  2 

Lay  off  jETJ=-f— .     It  is  obvious  then  that   G  lies  at  a  point 
a 

such  that  Jg-logLH'P'.     By  using  a  drawing  scale  of  1:2, 

with  the  point  J  as  the  zero  point,  JG  may  be  graduated  to  repre- 
sent the  I.  H.  P.  on  a  logarithmic  scale,  such  that  for  any  two 
values  of  P  and  R,  falling  on  their  respective  scales  at  E  and  F, 
the  corresponding  I.  H.  P.  lies  on  the  scale  JG,  at  a  point  G  where 
this  scale  intersects  with  the  mid  point  of  the  straight  line  joining 
E  and  F. 

An  instrument  constructed  in  this  manner  may  be  adapted 
for  general  use  by  making  the  scale  of  I.  H.  P.  adjustable  in  a 
vertical  line.  The  value  of  HJ,  or  Je,  corresponding  to  the  particu- 
lar cylinder  of  the  engine  for  which  it  is  desired  to  use  the  instru- 
ment is  then  read  downward  from  J,  and  the  scale  of  I.  H.  P.  set 
with  the  proper  value  of  k  falling  at  H.  The  instrument  is  then 
ready  for  use.  When  constructed  for  use  in  calculating  the  indi- 
cated horse  power  of  the  main  engines,  the  various  values  of  log  fc 
may,  for  convenience,  be  laid  off  and  marked  for  each  end  of  each 
cylinder,  instead  of  in  the  form  of  a  graduated  scale.  In  order  to 
make  the  diagram  more  compact,  the  base  line  may  also  be  moved 
upward,  corresponding  to  the  minimum  values  of  P  and  R  that  will 
be  obtained  in  practice. 


MEASUREMENT  OF  POWER  161 

The  diagram  in  Fig.  90  is  laid  down  for  a  value  of  A;  =  16. 8, 
corresponding  to  a  cylinder  25  inches  in  diameter  and  2-ft.  stroke. 

Brake  Horse  Power. — This  term  is  generally  applied  to  the  horse 
power  actually  transmitted  to  the  shaft  and  is  so-called  from  the 
brake  which  absorbs  and  measures  the  power  transmitted.  Shaft 
Horse  Power  is  equivalent  to  the  brake  horse  power,  but  it  is 
measured  in  transmission  without  being  absorbed  by  the  apparatus 
used.  This  term  is  used  by  marine  engineers  to  designate  the 
power  delivered  to  the  propeller.  The  power  of  a  marine  turbine, 
measured  by  the  torsion  meter,,  is  shaft  horse  power. 

Absorption  Dynamometers. 

The  Prony  Brake. — This  is  the  most  common  form  of  absorp- 
tion dynamometer.  Its  construction  is  simple  and  it  is  usually 
extemporised  when  needed  for  the  test  of  an  engine. 

Eef erring  to  Fig.  91  two  wooden  beams  are  clamped  together, 


T 

\G 


FIG.  91. 


on  a  friction  wheel  carried  by  the  shaft  A,  by  bolts  (7(7.  DD  are 
stops  to  prevent  the  beam  turning  through  more  than  a  small 
angle  when  the  shaft  is  rotated.  The  long  end  of  the  lever  G  rests 
on  a  platform  scale,  while  the  short  end,  Ff  may  or  may  not  carry 
a  hook  on  which  weights  are  hung  to  balance  the  overhanging 
weight  of  the  long  end. 

Suppose  the  shaft  turning  to  the  left.  If  the  bolts  CO  be 
tightened,  there  is  increased  friction  on  the  brake  wheel  with 
corresponding  increased  pressure  at  G.  If  the  weight  of  the  beam 
is  exactly  balanced  at  F,  the  pressure  at  G  multiplied  by  the  length 


162  EXPERIMENTAL  ENGINEERING 

of  the  arm  a  is  the  moment  which  must  be  overcome  in  turning  the 
shaft.  In  one  revolution  the  work  done  =  Pxax27r  and  the  brake 
horse  power, 

TJ      TJ      T>   —    ^a  XPXR 

33000        ' 

where  a  is  the  length  of  the  arm  in  feet,  P  is  the  pressure  at  G  in 
pounds,  and  R  is  the  number  of  revolutions  per  minute. 

The  Water  Brake.— The  friction  wheel  and  band  of  the  Prony 
brake  may  be  replaced  by  a  runner  and  casing  similar  to  the  parts 
of  similar  name  in  a  centrifugal  pump.  The  blades  on  the  runner 
are  specially  designed  to  give  an  inefficient  pump  and  when  water 
is  admitted,  the  power  of  the  engine  is  dissipated  in  churning  the 
water,  and  this  effect  is  greatly  increased  by  restricting  the  flow. 
The  casing  is  balanced  on  bearings  which  permit  a  slight  rotary 
movement.  An  arm  on  the  casing  has  its  end  resting  on  a  plat- 
form scale  and  the  tendency  of  the  casing  to  rotate  is  measured  by 
the  pressure  on  the  scale.  The  power  is  calculated  in  the  same 
manner  as  for  the  Prony  brake. 

Small  water  brakes  are  in  use  in  the  laboratory  for  measuring 
the  power  of  small  engines.  They  are  manufactured  for  testing 
large  steam  turbines  and  motors  up  to  a  capacity  of  several  thousand 
horse  power. 

Electric  Brake. — A  dynamo  may  be  fitted  to  be  used  as  a  brake. 
The  armature  shaft  is  connected  to  the  engine  under  test.  The 
field  is  mounted  on  bearings  so  that  it  can  revolve  freely  through 
a  small  angle  about  the  armature  shaft  and  has  a  brake  arm  at- 
tached to  it.  When  the  dynamo  is  operated  the  power  exerted 
tends  to  rotate  the  armature  and  is  measured  as  in  the  case  of  the 
Prony  brake. 

Electric  Horse  Power. — When  an  engine  is  used  to  drive  a  dy- 
namo in  regular  service  the  output  of  the  dynamo  is  a  measure  of 
the  work  done,  and  is  obtained  by  reading  the  voltmeter  and 
ammeter.  Volts  X  amperes  =  watts.  Since  1  horse  power  =  746 
watts,  we  have 

^     ,  .     ,  volts  X  amperes  , .  x 

Electric  horse  power  =          —       l      -  .  (1) 


MEASUREMENT  OF  POWER 


163 


Remembering  that  the  efficiency  of  a  machine  = 
useful  work  done 


total  energy  received, 


we  have 


Efficiency  of  the  dynamo=  gectric  horge  power 

snait  horse  power 


(2) 


Therefore  dividing  (1)  by  the  efficiency  of  the  dynamo,  which 
should  be  known  as  the  result  of  previous  tests,  we  may  obtain  the 
shaft  horse  power.  By  further  dividing  the  result  thus  obtained 
by  the  known  efficiency  of  the  engine,  we  obtain  a  close  approxima- 
tion to  the  indicated  horse  power. 

This  may  be  better  understood  by  reference  to  the  accompany- 
ing diagram,  Fig.  92,  in  which 

T)      TT     T> 

EI  =  Efficiency  of  engine  =     '     '     '  , 


or 


E2  =  Efficiency  of  dynamo  = 

E.  H.  P. 
I.H.  P.  ' 

E.  H.  P. 


E.  H.  P. 


I.H.P.= 


Engine 

Shaft 

Dynamo 
E.  H.  P. 

I.H.P. 

B.  H.  P. 

FIG.  92. 

Transmission  Dynamometers. 

Under  this  head  is  classed  a  wide  variety  of  instruments  used 
for  the  determination  of  the  power  transmitted  by  a  shaft  while 
employed  in  doing  the  work  for  which  it  was  designed.  No  work 
is  absorbed  by  such  instruments  other  than  that  necessary  to  move 
them. 

Belt  Dynamometers, — 'Where  power  is  transmitted  by  a  belt  if 
it  is  arranged  to  measure  the  tension  on  each  side  of  the  belt,,  the 


164 


EXPERIMENTAL  ENGINEERING 


difference  in  such  tensions  multiplied  by  the  speed  of  the  belt  gives 
the  work  done.  Owing  to  the  loss  of  power  due  to  the  stiffness  of 
the  belt,  and  the  uncertainty  due  to  slipping,  such  dynamometers 
have  not  been  used  extensively. 

The  Kenerson  Transmission  Dynamometer. — This  instrument, 
the  invention  of  Prof.  Kenerson,  of  Brown  University,  is  used  for 
measuring  the  power  transmitted  by  a  shaft.  Pig.  93  shows  a 


1*o  Gage 


FIG.  93. — Dynamometer   Shown   in    Section. 

sectional  view  of  the  instrument,  while  Figs.  94  and  95  show  the 
instrument  as  applied  to  the  driving  shaft  of  an  automobile.  The 
lettering  of  corresponding  parts  in  Figs.  93  and  95  is  the  same. 

The  couplings  A  and  B,  each  keyed  to  its  respective  shaft,  are 
held  together  loosely  by  the  stud  bolts  C.  The  holes  in  the  flange  A 
are  larger  than  the  studs  C,  so  that  these  studs  have  no  part  in 
transmitting  power  from  one  shaft  to  the  other.  The  power  is 
transmitted  from  A  to  B  through  the  agency  of  the  latches  L,  four 
of  which  are  arranged  around  the  circumference  of  the  flange  B. 
These  latches  are  mounted  and  are  free  to  turn  on  the  studs  E. 
The  two  fingers  of  the  latches  engage  the  studs  F  on  the  flange  A. 
On  the  ends  of  each  latch  are  knife  edges  parallel  to  the  stud  about 


MEASUREMENT  OF  POWER 


165 


s 


166 


EXPERIMENTAL  ENGINEERING 


which  the  latch  turns.  For  either  direction  of  rotation  of  the  flange 
A  the  latches  L,  which  are  in  effect  double  bell-crank  levers,  will 
exert  a  pressure  on  the  disc  G,  tending  to  force  it  axially  along  the 


FIG.  96. 


hub  of  the  coupling  B,  and  this  pressure,  it  will  be  seen,  is  pro- 
portional to  the  torque. 

Between  the  end-thrust  ball,  or  roller,  bearings  MM,  is  held 
the  stationary  ring  S,  which  is  the  weighing  member.  0  is  a  thrust- 
collar  screwed  on  the  hub  of  B,  and  'P  is  its  check  nut,  which  is 


MEASUREMENT  OF  POWER 


167 


ordinarily  pinned  to  the  hub  when  in  position.  The  stationary 
member  S,  in  the  form  of  a  ring  surrounding  the  shaft,  is  pre- 
vented from  rotating  by  fastening  to  some  fixed  object  the  attached 
arm  shown  in  the  view  (Fig.  94)  of  the  assembled  instrument.  In 
this  ring  is  an  annular  cavity  covered  by  a  thin,  flexible  copper 
diaphragm  D,  against  which  the  ball-race  of  one  of  the  thrust-bear- 


PIG.  97. 

ings  presses.  The  edge  of  this  ball-race  is  slightly  chamfered  to 
allow  some  motion  to  the  diaphragm.  The  cavity  is  filled  with  a 
fluid,  such  as  oil,  and  connected  by  means  of  a  tube  to  a  gage. 
The  oil  pressure  measured  by  the  gage  is  proportional  to  the  pres- 
sure between  the  thrust-bearings,  which  in  turn  is  proportional  to 
the  torque. 

The  Emerson  Power  Scale. — This  instrument  is  made  to  go  on  a 
belt-driven  shaft  next  to  the  loose-belt  pulley.  The  two  studs  CC, 
shown  in  Figs.  96  and  97,  engage  with  the  spokes  of  the  loose 


168 


EXPERIMENTAL  ENGINEERING 


pulley  and  cause  the  plate  E  to  run  with  it.  E  revolves  freely  ex- 
cept for  the  bolt  G  which  may  be  pushed  out  to  engage  with  it  by 
means  of  the  slide  H.  When  this  is  done  the  rim  of  the  apparatus 
is  made  to  turn  and  through  the  system  of  levers,  shown  in  Fig.  96, 
this  motion  is  transmitted  to  the  shaft.  These  levers  are  a  part  of 
a  weighing  mechanism,  very  similar  in  construction  to  that  con- 
tained in  standard  platform  scales.  When  the  shaft  is  in  opera- 
tion the  torque  is  registered  by  the  weighing  mechanism.  This, 
multiplied  by  the  revolutions  per  minute  and  the  constant  of  the 
instrument,  gives  the  power. 

The  revolutions  of  the  shaft  are  registered  on  the  dial  shown  in 
Fig.  96. 

As  used  in  the  laboratory  in  connection  with  an  explosion  en- 
gine, the  apparatus  is  not  in  any  way  secured  to  the  line  of  shaft- 
ing. The  line  of  shafting  projects  a  short  distance  into  the  shaft  of 
the  power  scale  to  act  as  a  support  and  a  guide.  The  shaft  of  the 
power  scale  ends  in  a  sleeve  that  fits  over  the  end  of  the  line  shaft. 

The  power  is  worked  out  by  knowing  the  radius  of  the  first 
transmission  of  the  power  and  the  revolutions.  For  the  special 
apparatus  in  the  laboratory  it  is  as  follows : 

'Circumference  of  point  of  application  of  power.  .   6  feet. 

Revolutions    a 

Weight  read  on  scale b 

6xax&       Circ.  X  Wt.  X  Rev.     T  TT  T> 


33000 


33000 


The  table  below  gives  the  capacity  at  100  revolutions: 


Hole, 
Inches. 

Greatest 
Diameter. 

Weight. 

Capacity. 

Circle  of 
Graduation. 

No.  2 

26  inches. 

260  Ibs. 

27  h.  p. 

6  ft. 

An  allowance  must  be  made  for  the  reading  of  the  power  scale 
when  running  with  no  resistance  at  each  number  of  revolutions. 
This  must  be  tested  and  a  table  made.  The  net  pressure  is  the  dif- 
ference between  that  under  power  and  light. 


MEASUREMENT  OF  POWER 


169 


Torsionmeters. — When  power  is  transmitted  through  an  elastic 
shaft,  within  its  elastic  limit,  the  shaft  is  twisted  through  an  angle, 
the  amount  of  such  distortion  depending  on  the  size  of  the  shaft 
and  the  power  transmitted.  In  any  given  shaft  there  is  a  fixed 
proportion  between  the  amount  of  twist  and  the  applied  moment  of 
rotation.  Having  calibrated  the  shaft,  it  remains  to  provide  an 
instrument  to  measure  the  amount  of  its  distortion  when  running. 
From  this  and  the  revolutions  of  the  shaft  the  power  is  calculated. 


FIG.  98. 

Calibration  of  Shafting. — Previous  to  being  placed  in  position  in 
the  ship,  the  shaft  should  be  calibrated.  This  should  be  done  by 
coupling  the  various  lengths  together,  including  the  length  over 
which  the  torsion  is  to  be  measured,  placing  it  in  bearings  and  pro- 
ceeding in  the  following  manner:  One  end  is  clamped  rigidly  so 
that  it  cannot  turn,  and  to  the  other  is  attached  a  lever  to  the  end 


170  EXPERIMENTAL  ENGINEERING 

of  which  weights  are  attached.  A  pointer  is  also  attached  to  the 
free  end  of  the  shaft,  about  6  or  8  feet  in  length  and  stiff  enough 
so  that  it  will  not  bend  under  its  own  weight.  A  paper  scale  is 
placed  under  the  end  of  the  pointer  to  register  its  movement  in 
inches. 
Eeferring  to  Fig.  98  let 

c  —  movement  of  the  pointer  in  inches  under  the  influence  of 

the  added  weight  W,  applied  to  arm  a. 
r— length  of  pointer  in  inches. 

I  —  length  of  shaft  being  twisted,  exclusive  of  couplings. 
L  =  length   of   portion   of    shaft   on    which   torsionmeter   is 

applied. 

R  —  radius  of  arc  on  which  torsionmeter  readings  are  taken. 
C  =  reading  of  torsionmeter  corresponding  to  movement  of 

pointer  c. 
Extending  the  lines  of  the  figure  as  shown,  we  have 


/  C1         r 

=  -s-  and  —x-  —  -r=- 


from  which 


and 


C       LXR     c  L_      JR_ 

c      '  IXr   '  X    I    X    r 


the  angle  of  torsion  of  length  L  of  the  shaft,  expressed  in  circular 
measure. 

The  moment  M,  caused  by  the  pull  W  on  an  arm  of  length  a  — 
Wxa.  From  the  results  of  the  calibration  experiments,  a  curve 
is  constructed,  the  ordinates  giving  the  values  of  M  in  foot  pounds 
and  the  abscissae  the  corresponding  readings  of  the  torsionmeter. 
From  this  curve  the  moment,  corresponding  to  any  reading  of  the 
torsionmeter,  is  obtained. 

The  shaft  horse  power  (S.  H.  P.)  is  equal  to 

2  X  TT  x  M  X  Revs.  _  M  X  Revs. 
33000  ~      5252      ' 


MEASUREMENT  OF  POWER  171 

Horse  Power  from  the  Torsionmeter  Without  Calibration  of 
Shafting. — From  applied  mechanics  we  have  the  angle  of  torsion 
for  a  shaft  within  the  elastic  limit, 

K/f  v  T  fi 

$—~W — T~~I  =  ~£rc\  >  wnere  #=the  angle  of  torsion  meas- 
LJ  x  1  X  d       ooU 

ured  in  degrees. 

M= the  twisting  moment  in  inch  pounds. 
L  —  length  of  shaft  in  inches. 

E  =  modulus  of  elasticity  of  the  material  of  the  shaft. 
d  =  diameter  of  shaft  in  inches. 

I  —  moment  of  inertia  of  the  section  about  the  axis=  ^ 

Xd3  for  solid  shafts  or^f — ~7  1    )  where  d  =  out- 
16  \       d       ) 

side  diameter  and  di  =  inside  diameter  of  shaft,  both 
in  inches. 

It  is  more  convenient  to  express  M  in  foot  pounds.  Making  this 
change,  we  have 


,,-_  ir        _  7r  fi 

360xl2x£      ~  16  X 


for  solid  shafts,  or 

M-  * 

'   16 

for  hollow  shafts. 

Substituting  these  values  of  M  in  the  above  expression  for  horse 
power,  we  have  for  solid  shafts 
M  xRevs. 


33000  ~  360  X  16x12x33000  XL' 

For  high-grade  steel,  such  as  is  used  for  the  shafting  of  naval 
vessels,  E  is  approximately  11,750,000. 
Substituting  this  and  evaluting,  we  have 

Q   TT   p_<24X0X  Revs. 

for  solid  shafts  and  similarly 

S   H  P  --(^4 


3.13XL 

for  hollow  shafts,  the  terms  being  named  as  before. 


172 


EXPERIMENTAL  ENGINEERING 


In  any  particular  installation  of  a  torsion  meter,  these  formulae 
are  applicable,  the  expression  in  each  case  taking  the  form 

S.  H.  P. 


where  K  is  a  constant  and  C  is  the  torsionmeter  reading.  This  ex- 
pression is  general  and  applies  in  all  cases  where  C  is  proportionate 
to  the  angle  of  twist,  whether  it  be  measured  in  degrees,  or  in 
linear  units  on  an  arc  of  given  radius. 


FIG.  99. 

Results  obtained  by  calculation  from  the  modulus  of  elasticity 
approximate  closely  to  those  obtained  by  calibration,  their  accuracy 
depending  of  course  on  the  correctness  of  the  figure  used  for  the 
modulus. 

The  Navy  Department  requires  the  shafting  of  its  vessels  to  be 
calibrated  before  installation.  This  is  more  necessary  with  hollow 
than  with  solid  shafting,  since  for  the  formula  for  hollow  shafting 
to  be  correct,  the  hole  must  be  centered  with  exactness. 

The  Denny-Johnson  Torsiometer. — Two  bronze  wheels,  A  and 
B,  Fig.  99,  are  placed  on  the  shaft  at  a  definite  and  known  distance 
apart,  the  distance  being  as  great  as  possible.  On  each  of  these 
wheels  a  permanent  magnet,  with  a  sharp  chisel-shaped  edge  is 


MEASUREMENT  OF  POWER  173 

fixed  radially,  at  the  periphery  of  the  wheel,  and  with  the  sharp 
edge  parallel  to  the  shaft.  Under  one  of  these  wheels,  soft  iron 
sector  cores  are  placed,  wound  with  a  series  of  coils  of  very  thin 
wire,  so  fine  indeed  that  each  coil,  with  its  dividing  wall  in  one  of 
the  sectors,  only  occupies  a  space  of  0.02  inch.  Under  the  other 
wheel  similar  sectors,  or  inductors,  as  they  are  called,  are  fitted, 
but  in  this  case  the  coils  are  further  apart,  viz.,  0.2  inch. 

In  the  lower  part  of  Fig.  99  is  shown  the  arrangement  of  recording 
boxes.  For  each  shaft  this  consists  of  two  circles,  fitted  with  con- 
tact studs  and  movable  contact  arms;  the  one  marked  E  is  con- 
nected with  the  inductor  at  the  wheel  next  the  propeller  and  has 
six  contacts.  That  is  to  say,  each  of  the  six  coils,  spaced  0.2  inch 
apart,  is  connected  to  one  of  the  studs.  The  other  one,  marked  F, 
has  thirteen  contact  studs,  connected  to  the  thirteen  coils,  spaced 
0.02  inch  apart,  on  the  inductor  at  the  turbine  end  of  the  shaft. 

The  magnets  are  so  placed  that  when  passing  the  inductors,  cur- 
rents of  opposite  potentiality  are  induced.  These  are  carried  to  a 
telephone  receiver,  and  when  either  magnet  passes  an  inductor  a 
click  is  heard.  If  they  pass  simultaneously,  the  two  currents  tend 
to  neutralize  one  another  and  the  single  click  is  greatly  diminished, 
or  vanishes  altogether.  There  are  two  resistance  boxes,  not  shown 
in  the  figure,  for  throwing  into  series  with  the  differential  wind- 
ings of  the  telephone  receiver  and  the  two  inductor  circuits,  which 
circuits  must  be  accurately  balanced  before  absolute  silence  can  be 
obtained  in  the  receiver. 

To  take  a  reading  after  the  instrument  is  once  set,  and  the 
resistance  of  the  two  telephone  circuits  is  adjusted,  all  that  is  neces- 
sary is  to  turn  the  movable  arm  on  scale  F  round  the  various  studs 
until  there  is  silence  in  the  telephone,  when  the  amount  of  torsion  is 
immediately  read  of?  the  scale.  If  no  such  position  be  found,  it 
means  that  the  shaft  is  being  twisted  more  than  is  covered  by  this 
scale ;  the  arm  E  is  then  turned  to  the  first  contact,  and  the  arm  F 
is  again  swept  round  the  circuits.  If  silence  be  still  not  obtained, 
the  arm  E  is  turned  to  the  second  contact,  and  so  on,  the  combined 
range  of  the  scales  being  altogether  1.24  inches,  which  is  more  than 
sufficient  to  measure  the  maximum  torque  usually  obtained.  From 
torsion  experiments  on  the  shaft,  made  previous  to  its  being  fitted 
12 


174  EXPERIMENTAL  ENGINEERING 

in  the  ship,  the  factor  by  which  this  reading  is  to  be  multiplied  is 
obtained,  and  the  power  gotten  by  a  simple  multiplication. 

The  instrument  is  made  for  one,  two,  three,  and  four  shafts; 
a  group  of  scales  and  resistances,  as  described  above,  being  required 
for  each  shaft,  all  mounted  on  one  panel.  By  means  of  the  contact 
arms  and  studs  the  various  shafts  are  thrown  into  circuit  with  their 
receivers  and  readings  taken  from  all  the  shafts  in  a  very  short  time. 
The  sound  in  the  receiver  at  usual  revolutions  is  so  distinct  that 
even  an  untrained  observer,  after  a  few  minutes'  practice,  can  get 
perfectly  accurate  results,  and  powers  transmitted  can  be  obtained 
from  moment  to  moment.  The  instruments  are  mounted  in  a  room 
in  some  quiet  part  of  the  ship  where  the  observer  will  be  free  from 
interruption. 

Instrument  for  Low  Speeds. — The  above  instrument  is  not  suited 
for  very  low  revolutions,  as  the  induced  current  becomes  too  weak 
to  make  a  distinct  sound  in  the  telephone;  but  it  is  suitable  down 
to  about  100  revolutions  per  minute.  For  lower  revolutions  a 
somewhat  similar  arrangement  has  been  used  in  which  the  two 
wheels  keyed  on  the  shaft  were  on  insulating  material,  and  each  had 
a  contact  point  arranged  at  its  periphery  in  such  manner  that  the 
point  made  a  momentary  contact  with  a  metallic  tongue  or  brush 
once  in  each  revolution.  The  contact  points  were  connected  to  the 
shaft,  and  the  metal  brushes  to  a  battery  and  a  telephone  receiver. 
The  method  adopted  was  to  first  adjust  the  brushes  so  that  both 
made  contact  with  the  points  simultaneously  when  the  shaft  was 
revolving,  but  transmitting  no  power.  When  transmitting  power 
the  shaft  was  of  course  subject  to  torsion  and  thus  the  brushes  were 
put  out  of  simultaneous  contact.  One  of  the  brushes  was  then 
moved  arouad  its  disc  concentrically,  until  simultaneous  contact  was 
once  more  established.  The  amount  of  this  shift  gave  a  measure  of 
the  torque  on  the  shaft,  and  to  ascertain  the  correct  amount  of  this 
shift  the  telephone  receiver  was  placed  to  the  ear,  no  sound  being 
heard  except  when  both  brushes  were  in  contact  with  the  respective 
contact  points. 

This  apparatus,  though  more  simple  than  that  above  described, 
is  not  applicable  on  shafting  running  at  high  speed,  since  it  is  im- 
possible to  obtain  the  make  and  break  with  certainty.  Experiments 


MEASUREMENT  OP  POWER 


175 


176  EXPERIMENTAL  ENGINEERING 

with  it  on  high  speed  shafting  led  to  the  perfection  of  the  Torsio- 
meter,  above  described. 

The  Denny-Johnson  Torsiometer  is  largely  used  on  the  earlier 
turbine-driven  vessels.  It  is  accurate  and  satisfactory  when  care  is 
taken  with  its  installation.  The  numerous  electrical  connections 
sometimes  give  trouble,  chiefly  through  short  circuiting  with  salt 
water. 

The  Bevis-Gibson  Flashlight  Torsionmeter. — Eeferring  to  Fig. 
100,  the  shaft  has  two  discs  clamped  on  it  in  positions  as  far  apart 
as  practicable.  These  discs  are  each  pierced,  around  a  circum- 
ference of  the  same  radius,  with  twelve  radial  slots.  Behind  each 
of  the  discs  there  is  a  fixed  support  above  the  shaft.  On  one  of 
these  a  lamp  is  placed  and  on  the  other  there  is  an  eye  piece,  with 
shutter,  mounted  on  a  movable  "  finder."  Both  lamp  and  eye 
piece  are  at  the  same  distance  from  the  center  of  the  shaft. 

When  the  shaft  is  at  rest,  with  the  finder  in  the  zero  position,  the 
lamp,  similarly  placed  slots  in  the  two  discs,  and  the  eye  piece, 
are  in  line,  and  the  light  from  the  lamp  is  seen  by  the  observer 
through  the  eye  piece.  If  the  shaft  were  turned  rapidly,  without 
torsion,  the  light  would  be  seen  as  a  continuous  ray. 

When  the  shaft  is  transmitting  power,  the  relative  position  of  the 
two  discs  is  changed,  and  the  lamp  and  the  eye  piece  are  no  longer 
in  line  with  similarly  placed  slots,  so  that  the  ray  is  cut  off.  To 
find  it  again  it  is  necessary  to  move  the  finder  along  a  graduated 
scale,  fitted  with  a  vernier  for  close  reading.  The  amount  of  move- 
ment required  to  bring  the  ray  again  into  coincidence  is  propor- 
tionate to  the  angle  of  torque. 

Fig.  101  shows  the  principle  of  operation  and  the  method  of  pick- 
ing up  the  deflected  ray  of  light  by  moving  the  finder. 

The  flash  light  torsionmeter  is  free  from  complicated  mechanical 
parts,  which  in  some  other  torsionmeters  introduce  error  through 
lost  motion.  There  may  be  considerable  variation  in  the  readings, 
due  to  the  breadth  of  the  beam  of  light  as  seen  through  the  eye 
piece,  but  in  the  hands  of  a  careful  observer  very  accurate  results 
can  be  obtained  with  it.  The  edge  of  the  beam  of  light  should  be 
caught,  first  on  one  side,  then  on  the  other,  the  mean  of  the  two 
giving  the  desired  reading. 


MEASUREMENT  OF  POWER 


177 


The  instrument  does  not  give  a  permanent  record  and  it  is  not 
always  possible  to  find  for  it  the  amount  of  space  in  the  fore  and 
aft  direction  that  it  requires. 

The  Fottinger  Torsionmeter. — Fig.  102  shows  the  working  parts 
of  this  instrument.  The  ring  B  with  two  arms  and  the  ring  D  at 
the  after  end  of  the  steel  sleeve  C  are  both  clamped  firmly  to  the 
shaft.  On  the  forward  end  of  the  sleeve  is  a  ring  A  similar  to  B. 
There  is  a  clearance  between  this  ring  and  the  shaft,  and  it  is  cen- 
tered on  B  by  means  of  radial  centering  rods  having  knife  edges 
on  each  end.  The  sleeve  C  and  ring  A  act  as  a  rigid  mass  and  turn 


Find* 


2  PLAN. 

Shaft.  Transmitting  Power 
Light  obscured. 


3   PLAN, 

Shaft,  Transmitting  Power 

"  Finder"  moved  through  an  angle  equal  to  amount  of  Torque 
Light  visible 


FIG.  101. 

with  that  part  of  the  shaft  to  which  D  is  clamped.  When  a  tor- 
sional  stress  is  applied  to  the  shaft  the  ring  B  twists  relative  to 
A.  Through  a  flexible  link  E,  a  bell  crank  H  pivoted  on  A,  and  a 
link  J  connected  to  the  magnalium  ring  N  which  floats  on  the  sleeve 
C,  this  relative  twist  is  magnified  and  changed  to  a  fore-and-aft 
motion.  A  shoe  P  is  brought  into  contact  with  a  flange  on  the 
magnalium  ring,  and  the  fore-and-aft  motion  of  the  ring  is  again 
magnified  and  indicated  by  a  pointer  Q  on  a  scale  T. 

The  constant  for  the  machine  is  found  by  calibrating  the  shaft 
and  torsionmeter  in  the  shop  previous  to  installation  in  the  ship. 
The  after  end  of  the  shaft  is  bolted  to  a  fixed  flange.  The  forward 
end  rests  in  a  roller  bearing  and  on  the  forward  flange  is  bolted  a 
double  lever.  A  known  twisting  moment  is  applied  to  this  lever 


178 


EXPERIMENTAL  ENGINEERING 


MEASUREMENT  OF  POWER 


179 


and  the  corresponding  torsionmeter  readings  are  observed.  From 
the  slope  of  the  line  plotted  between  torsionmeter  readings  and 
torque  a  constant  is  obtained  such  that 


in  which  H.  P.  =  shaft  horse  power,  R  =  revolutions  of  the  shaft 
per  minute,  and  F=  torsionmeter  reading. 

This  torsionmeter  requires  but  little  space  and  gives  a  direct  in- 
dication of  the  torque.  A  later  form  is  designed  to  give  a  perma- 
nent record.  It  is  open  to  the  objection  that  the  numerous  levers 
and  joints  introduce  lost  motion  with  corresponding  errors  of  ob- 
servation. 


FIG.  103. — Torsionmeter  Mounted  Complete  on  Shaft. 

The  Hopkinson-Thring  Torsionmeter. — The  principal  of  this 
apparatus  is  a  differential  one,  and  consists  in  the  observation  of 
the  twist  between  two  points  on  the  shaft  by  means  of  two  beams 
of  light  projected  on  to  a  scale  from  a  fixed  and  a  movable  mirror. 
The  beam  projected  on  the  scale  by  the  fixed  mirror  is  taken  as  the 
zero  point,  while  the  beam  projected  by  the  movable  mirror  indi- 
cates the  amount  of  torque  on  the  shaft.  Both  mirrors  revolve  with 
the  shaft,  but  even  at  moderate  speeds  the  reflections  appear  as 
continuous  lines  of  light  across  the  scale. 

The  torsionmeter  is  shown  in  Fig.  103,  mounted  complete  on  a 


180  EXPERIMENTAL  ENGINEERING 

shaft,  and  the  scale  box  in  Fig.  104,  while  a  diagrammatic  arrange- 
ment of  the  complete  apparatus  is  shown  in  end  elevation  and  plan 
in  Figs.  105  and  106  respectively.  A  collar  A,  clamped  to  the 
shaft  of  which  the  torque  has  to  be  measured,  is  provided  with  a 
flange  projecting  at  right  angles  to  the  shaft  and  an  extension 
(Fig.  106.) 

A  sleeve  B  (Fig.  106),  provided  with  a  similar  flange  and  ex- 
tension at  one  end,  is  clamped  at  its  further  end  on  to  the  shaft  in 
such  a  manner  that  its  flange  is  close  to  that  on  the  collar  A,  while 
its  entension  overlaps  that  of  the  collar  A,  on  which  it  is  supported 
to  keep  it  concentric.  Both  the  collar  and  sleeve  are  quite  rigid, 
and  it  is  obvious  that  when  the  shaft  is  twisted  by  the  transmission 


FIG.  104. — Scale  Box  with  Lamp,  for  Torsionmeter. 

of  power,  the  flange  on  the  sleeve  B  will  move  relatively  to  that  on 
the  collar  A,  the  movement  being  equal  to  that  between  the  two 
parts  of  the  shaft  on  which  these  fittings  are  clamped.  This  move- 
ment is  made  visible  by  a  system  of  torque  mirrors  mounted  be- 
tween the  two  flanges,  which  reflects  a  beam  of  light,  projected  from 
a  lantern,  on  to  a  scale  divided  in  a  suitable  manner  on  ground 
glass. 

This  system  of  torque  mirrors  consists  of  a  mounting,  pivoted 
top  and  bottom  on  one  or  other  of  the  flanges,  in  which  two  mirrors' 
are  arranged  back  to  back.  This  mounting  is  provided  with  an 
arm,  the  end  of  which  is  connected  by  a  flat  spring  to  an  adjustable 
stop  on  the  other  flange.  Any  relative  movement  of  the  two  flanges 


MEASUREMENT  OF  POWER 


181 


TORQUE  MIRROR 


LAMP 


GLASS 


-ZERO  M'RRORS 


FIG.  105. 


LLAR  A 


FIG.  106 


182  EXPERIMENTAL  ENGINEERING 

will  turn  the  torque  mirror  and  thereby  cause  the  beam  of  light  to 
move  on  the  scale,  the  deflection  produced  being  directly  propor- 
tional to  the  torque  applied  to  the  shaft.  Hence,  if  the  rigidity  of 
the  material  and  the  number  of  revolutions  per  minute  are  known, 
the  H.  P.  transmitted  can  be  readily  calculated. 

With  the  arrangement  described,  a  reflection  will  be  received  from 
each  mirror  at  every  half  revolution  of  the  shaft;  but  where  the 
torque  varies  during  a  revolution  (as  with  reciprocating  engines), 
a  second  system  of  mirrors  may  be  arranged  at  right  angles  to  the 
first  system,  so  that  four  readings  can  be  taken  during  one  revolu- 
tion ;  or,  if  two  scales  are  used,  eight  readings  can  be  taken. 

Fig.  105  shows  how  the  beam  of  light  reflected  by  the  mirror 
when  in  its  highest  position  passes  through  the  upper  part  of  the 
scale;  while  the  second  reflection  will  occur  when  the  mirror  is  in 
the  position  occupied  by  the  zero  mirror,  the  beam  of  light  passing 
through  the  lower  part  of  the  scale.  The  position  of  the  torque 
mirror  in  Fig.  106  is  such  that  the  reflected  beam  strikes  the  scale 
to  the  right  of  the  zero  line,  but  when  the  shaft  has  made  a  further 
half  revolution,  the  reflected  beam  from  the  other  mirror  will  strike 
the  scale  to  the  left  of  the  zero  line.  Obviously  the  deflection  on 
both  sides  should  be  equal. 

The  fixed  mirror  is  attached  to  one  of  the  flanges  (in  Fig.  106  to 
the  flange  of  the  sleeve  B).  This  must  be  adjusted  so  that  the  beam 
of  light  reflected  from  it  is  received  at  the  same  point  on  the  scale  as 
those  from  the  movable  mirrors  when  there  is  no  torque  on  the 
shaft.  To  facilitate  the  erection  and  adjustment  of  the  apparatus, 
the  box  containing  the  scale  and  carrying  the  lamp  is  fitted  with 
trunnions,  so  that  it  can  be  inclined  as  required. 

If  the  position  of  the  apparatus  becomes  altered  relatively  to  the 
scale  owing  to  the  warming  up  of  the  shaft  or  from  other  causes, 
this  is  indicated  immediately  to  the  observer  by  an  alteration  in  the 
position  of  the  zero  as  reflected  by  the  fixed  mirror.  Hence,  the 
zero  can  be  adjusted  by  moving  the  scale  so  that  its  zero  coincides 
with  the  reflection  from  the  fixed  mirror.  It  will  be  obvious  that  it 
is  not  necessary  to  move  the  scale,  as  the  mean  of  the  two  readings 
will  be  the  same.  It  will  readily  be  understood  that  a  movement  of 
the  torque  mirrors  can  only  occur  through  a  relative  movement  of 


MEASUREMENT  OF  POWER 


183 


the  two  flanges,  so  that  vibration  of  the  shaft  or  of  the  ship  will  not 
influence  the  readings. 

The  constant  of  the  instrument,  viz.,  the  factor  which,  when 
multiplied  or  divided  into  the  product  of  the  torsionmeter  reading 
and  the  revolutions,  gives  the  horse  power,  may  be  calculated  within 
2  or  3  per  cent,  if  the  section  of  shaft  within  the  instrument  is 
uniform.  A  direct  calibration  of  the  shaft  with  the  instrument  in 
position  is  recommended  before  the  former  is  put  into  the  ship. 
This  is  effected  readily  by  applying  a  known  twisting  couple. 

This  instrument  is  inexpensive  and  the  absence  of  complication 
makes  it  fairly  accurate,  but  there  is  no  permanent  record.  Con- 
siderable transverse  space  is  required  for  the  scales,  which  must  be 
darkened  to  observe  the  readings.  It  is  widely  used  on  vessels  of 
the  British  ISTavv. 


FIG.  107. 

The  Metten  Torsionmeter. — This  instrument  was  designed  by 
Chief  Engineer  Metten  of  the  Wm.  Cramp  &  Sons  Ship  and 
Engine  Building  Company  of  Philadelphia.  The  principal  parts 
are  shown  in  Fig.  107.  A  is  a  sleeve,  fitting  loosely  on  the  shaft 
at  the  end  shown,  and  rigidly  attached  to  the  shaft  at  the  opposite 
end.  This  sleeve  is  made  in  halves  for  convenience  in  assembling. 
Two  extension  arms,  Y,  are  attached,  forming  part  of  the  sleeve. 
One  of  these  is  for  attaching  to  the  mechanism,  while  the  other 
serves  merely  to  balance  the  apparatus.  B  is  a  disc  securely  fixed 
to  the  shaft,  close  to  the  arm  Y,  as  shown.  Pivoted  on  this  disc, 
at  Z,  is  a  very  light  frame,  Ff  carrying  two  knives,  K,  for  making 


184  EXPERIMENTAL  ENGINEERING 

the  record.  At  the  apex  of  frame  F  is  a  crank  pin,  S,  with  flat  con- 
necting link,  L,  to  a  pin,  P,  at  the  upper  end  of  Y.  The  pin  P  is 
eccentric  and  can  be  rotated  while  making  the  zero  adjustment  of 
the  instrument.  The  clamp,  C,  serves  to  hold  P  rigidly  in  position 
after  the  adjustment  is  made.  0  is  a  grease  cup  for  lubricating 
the  pivot  bearings  at  Z.. 

When  the  shaft  is  transmitting  power,  P  and  Y  tend  to  rotate 
slightly  with  reference  to  each  other.  The  frame,  F,  is  caused  to 
swing  about  Z,  the  proportions  of  the  frame  being  such  that  the 
knives,  K,  are  each  given  a  movement  fifteen  times  that  of  the  pin  8. 
One  knife  moves  from  the  zero  line  toward  the  center  of  the  shaft, 
while  the  other  moves  outward.  A  strip  of  paper  is  held  in  a  station- 
ary clamp  in  front  of  the  disc,  so  that  the  knives  in  passing  make 
cuts  in  the  edge  of  the  paper.  The  distance  between  these  cuts  will 
be  thirty  times  the  linear  movement  of  S,  and  is  a  direct  measure 
of  the  torque  in  shaft. 

The  constant  of  the  instrument  is  determined  in  a  manner  similar 
to  that  used  for  other  torsionmeters. 

Fig.  108  shows  the  table  for  holding  the  paper  on  which  records 
are  made  with  this  torsionmeter.  The  table  proper,  3,  is  on  a 
frame,  II,  secured  by  a  hinge  5,  to  the  fixed  base  I.  The  clamp,  8, 
holds  the  paper  firmly  with  its  edge  parallel  to  the  disc  of  torsion- 
meter.  The  set  screw,  6,  enables  the  distance  of  edge  of  paper 
from  face  of  disc  to  be  adjusted,  without  altering  the  setting  of 
the  paper  in  the  clamp. 

Torsionmeters  Compared  with  the  Indicator. — The  shaft  horse 
power,  obtained  by  the  use  of  the  torsionmeter,  can  be  compared 
with  the  indicated  horse  power  by  multiplying  the  latter  by  a  factor 
representing  the  efficiency  of  the  engine.  The  factor  0.92  is  used 
in  ordinary  calculations.  There  is  no  means  of  measuring  directly 
the  indicated  horse  power  of  a  turbine,  though  an  approximate  re- 
sult can  be  obtained  by  observing  the  fall  in  pressure  through  suc- 
cessive expansions,  by  means  of  gages  attached  to  the  turbine  stages, 
and  taking  corresponding  observations  to  determine  the  quality 
of  the  steam.  The  results  of  such  observations  are  entered  on  a 
temperature-entropy  chart,  thus  completing  a  diagram  representing 
the  cycle  of  heat  operations  in  the  turbine.  This  work  requires  con- 
siderable time  and  labor. 


MEASUREMENT  OF  POWER 


185 


FIG.  108. — Card  Table  for  Metten  Torsionmeter. 


186  EXPERIMENTAL  ENGINEERING 

Torsion  Readings  for  Reciprocating  Engines. — Perfect  results 
can  be  obtained  with  the  torsionmeter  only  where  the  turning  mo- 
ment is  uniform,,  as  it  is  in  turbine  driven  machinery.  In  a  re- 
ciprocating engine,  due  to  the  irregular  twisting  moment,  it  is 
difficult  of  application,  though  good  results  have  been  obtained  by 
fitting  as  many  as  six  sets  of  instruments  at  regular  intervals 
around  the  periphery  of  the  discs  placed  on  shafts.  By  taking 
the  mean  of  the  six  readings,  fairly  accurate  results  are  obtained. 
The  apparatus  has  been  thus  fitted  for  experimental  purposes  on  a 
few  vessels,  and  the  accuracy  of  the  torsionmeter  thus  demonstrated. 
The  arrangement  is  too  cumbersome  for  regular  application  on  a 
vessel  driven  by  reciprocating  engines. 

Curves  of  Chest  Pressures  and  Horse  Power. — For  a  vessel  in  com- 
mission curves  are  sometimes  constructed  showing  the  observed 
shaft  horse  power  for  given  values  of  the  steam-chest  pressure  and 
vacuum.  Such  curves  cannot  be  depended  upon  absolutely  for  es- 
timating horse  power  since  the  revolutions  will  vary,  depending  upon 
conditions  of  the  ship's  bottom  and  the  surface  of  propellers,  state 
of  the  sea,  etc.  Such  curves  are  of  great  value,  however,  in  indi- 
cating the  condition  of  the  turbine  blading.  Any  considerable  in- 
jury to  the  blading  would  be  marked  by  a  corresponding  decrease  in 
efficiency  which  would  be  indicated  on  examination  of  the  curves. 


CHAPTER  VIII. 
TESTING  MATERIALS  OF  CONSTRUCTION. 

Strength  of  Materials. — In  all  engineering  work  of  whatever 
character,  the  question  of  the  strength  of  the  materials  employed  is 
of  great  importance.  In  designing  the  machinery  of  a  war  vessel 
the  naval  engineer  is  confronted  with  the  necessity  of  reducing 
weights  as  much  as  possible,  but  he  must,  while  doing  this,  make 
the  machinery  of  sufficient  strength  to  stand  any  load  that  may  be 
put  upon  it  in  an  emergency.  The  materials  employed  must  be  of 
the  highest  grade  as  regards  strength,  and  of  such  uniform  character 
as  to  permit  the  reduction  of  the  factor  of  safety  as  much  as  pos- 
sible. Specifications  for  material  are  closely  drawn  and  much  of 
the  work  of  the  engineer  lies  in  the  inspection  of  such  material  to 
see  that  it  conforms  to  specifications. 

Stress  is  the  uniformly  distributed  force  applied  to  a  material. 
It  is  of  three  different  kinds :  -  longitudinal,  divided  into  tension 
and  compression;  transverse,  divided  into  shearing  and  bending; 
and,  twisting  or  torsional.  Stress  is  measured  by  the  number  of 
pounds  of  load  per  square  inch  of  cross  section. 

Strain  is  the  distortion  of  a  material  resulting  from  the  ap- 
plication of  stress  and  follows  in  its  classification  the  different  kinds 
of  stress  above  enumerated.  In  elastic  material  it  is  proportional  to 
the  stress. 

Elasticity  is  that  property  of  a  material  that  causes  it  to  return 
to  its  original  form  when  the  forces  acting  upon  it  have  been  re- 
moved. This  property  is  possessed  to  a  limited  extent  only,  by 
most  materials,  and  if  the  deformation,  or  strain,  exceeds  a  certain 
amount,  the  material  will  not  again  regain  its  original  form. 

Elastic  Limit  is  the  critical  point  beyond  which  the  material 
cannot  be  strained  without  a  permanent  distortion  or  set.  This 
point,  when  gradually  approached,  in  most  materials  is  indicated  by 
an  increase  in  the  increment  of  strain  due  to  a  constant  increment 
of  stress. 


188  EXPERIMENTAL  ENGINEERING 

Rigidity  or  Stiffness  is  the  property  by  means  of  which,  bodies 
resist  change  of  form. 

Coefficient  of  Ultimate  Strength  is  the  number  of  pounds  per 
square  inch  required  for  rupture,  and  is  obtained  by  calculation 
from  the  original  area  and  the  maximum  load. 

The  Coefficient  of  Strength  at  the  Elastic  Limit  is  the  number  of 
pounds  per  square  inch  acting  on  the  material  when  the  elastic 
limit  has  been  reached. 

Percentage  of  Elongation. — The  elongation  is  the  total  relative 
strain;  or  the  amount  that  a  piece  stretches  before  rupture.  It  is 
usually  expressed  as  a  percentage  of  the  original  length  of  the  test 
piece. 

Reduction  of  Area  of  Cross  Section. — After  fracture  of  a  test 
piece,  the  area  at  the  point  of  fracture  is  measured  and  the  reduction 
in  area  is  expressed  as  a  percentage  of  the  original  area. 

Modulus  of  Elasticity. — This  is  the  number  expressing  the  ratio 
of  the  stress  per  square  inch  to  the  deformation  per  inch  accom- 
panying that  stress,  within  the  elastic  limit.  It  is  denoted  by  E. 

Modulus  of  Resilience. — This  is  the  amount  of  work,  in  foot 
pounds,  done  in  deforming  a  cubic  inch  of  the  specimen  up  to 
elastic  limit.  It  is  equal  to  one-half  the  stress  per  square  inch  at 
elastic  limit  multiplied  by  the  total  elongation  in  feet  per  inch  of 
length  up  to  elastic  limit;  or  to  the  square  of  the  stress  at  elastic 
limit  divided  by  twice  the  value  of  E. 

Breaking  Load  and  Maximum  Load. — As  the  load  on  a  test  piece 
under  tension  is  gradually  increased,  the  piece  will  be  seen  to  visibly 
diminish  in  diameter,  this  diminution  being  at  first  uniformly 
distributed  along  the  whole  length  of  the  piece.  When  the  maxi- 
mum load  is  reached,  this  reduction  in  area  assumes  a  maximum 
amount  at  one  point,  where  a  distinct  thinning  takes  place.  The 
area  then  becomes  rapidly  reduced  at  this  point,  and  unless  the 
total  load  is  reduced,  the  load  per  unit  cross  section  becomes  greatly 
increased,  and  the  piece  will  no  longer  be  able  to  support  the  maxi- 
mum load.  By  careful  manipulation,  it  is  possible  to  so  reduce  the 
load  that  the  scale  beam  is  kept  balanced  up  to  the  point  of  actual 
rupture,  where  the  total  load  is  called  the  'breaking  load. 

The  Safe  Load  must  always  be  less  than  the  load  at  the  elastic 


TESTING  MATERIALS  OP  CONSTRUCTION 


189 


limit.  It  is  usually  taken  as  a  certain  fraction  of  the  ultimate  or 
breaking  load. 

The  Factor  of  Safety  is  the  ratio  of  breaking  load  to  safe  load. 

The  Strain  Diagram. — In  testing  a  piece  of  material,  if  we  lay 
off  the  strain  on  the  horizontal  axis,  to  a  scale  that  is  readily 
appreciable  to  the  eye,  and  the  corresponding  loads  as  ordinates  to 


FIG.  109. 


a  convenient  scale,  as  3000  or  5000  pounds  per  square  inch,  a  curve 
drawn  through  the  points  thus  plotted  gives  the  strain  diagram. 
Such  a  curve  is  drawn  autographically  on  the  testing  machine  and 
is  shown  in  Fig.  109.  The  strain  is  represented  by  distances  parallel 
to  OX,  the  load  as  a  certain  number  of  pounds  per  inch  parallel  to 
OY.  From  0  to  A  this  diagram  is  a  straight  line,  showing  that  the 
strain  is  proportional  to  the  stress.  At  A  there  is  a  sudden  increase 
in  strain  without  a  "marked  increase  in  load,  shown  by  the  curved 
line  from  A  to  B.  The  point  A  is  often  spoken  of  as  the  yield  point, 
13 


190  EXPERIMENTAL  ENGINEERING 

and  marks  the  elastic  limit.  In  curves  for  ductile  material,  taken 
autographically,  this  sudden  increase  of  strain  is  usually  accom- 
panied by  an  apparent  reduction  of  stress,  as  shown  by  the  curve 
from  B  to  C.  This  is  probably  due  to  the  fact  that  the  increase  in 
strain  is  so  great  that  the  scale  beam  falls  until  the  stress  is  in- 
creased. The  curve  then  continues  to  rise,  reaching  its  maximum 
height  at  D,  which  indicates  the  point  of  maximum  load.  From 
D  the  load  is  reduced  to  E,  which  indicates  the  breaking  load. 

The  Stress-Strain  Diagram. — This  diagram  is  sometimes  errone- 
Dusly  called  the  stress-strain  diagram.  The  ordinates  do  not  indi- 
cate stress,  but  load.  By  observing  and  plotting  the  area  of  cross 
section  of  the  test  piece  and  dividing  the  load  by  it,  the  amount  of 
stress  can  be  calculated  and  the  true  stress-strain  diagram  can  be 
thus  constructed. 

Testing  Machines. 

Machines  for  the  testing  of  materials  may  be  said,  in  general, 
to  consist  of  (1)  a  power  system,  by  which  stress  is  applied  to 
the  specimen,  and  (2)  a  weighing  system,  by  which  the  stress  ap- 
plied is  measured.  The  power  system  may  consist  of  a  train  of 
gears  or  an  hydraulic  cylinder,  either  of  which  may  be  operated  by 
power  or  by  hand.  The  weighing  system  usually  consists  of  a  sys- 
tem of  levers  and  a  poise  by  which  the  stress  is  balanced  as  on  an 
ordinary  pair  of  scales. 

The  form  of  testing  machine  in  general  use  is  that  in  which  the 
load  is  applied  through  a  train  of  gears  and  screws  operated  by 
power,  and  the  stress  is  measured  by  a  system  of  levers.  It  is  of 
the  vertical  type,  in  which  the  tensional  and  compressional  speci- 
mens are  held  in  a  vertical  position.  The  vertical  screws  connecting 
with  the  power  system  operate  a  movable  head,  to  which  the  lower 
end  of  the  tension  specimen  is  connected.  The  upper  end  of  the 
specimen  is  connected  to  the  upper  head,  which  is  a  part  of  the 
weighing  system  and  rigidly  connected  with  the  table  of  the  ma- 
chine, the  latter  resting  in  turn  on  the  lever  system.  In  compres- 
sional tests  the  specimen  is  placed  directly  between  the  movable 
head  and  the  table.  For  shearing  and  bending  tests  the  specimen  is 
held  between  supports  resting  on  the  table  and  the  stress  is  applied 
*s  for  compressional  tests. 


TESTING  MATERIALS  OF  CONSTRUCTION  191 

Kiehle  Screw  Power  Testing  Machines. — Fig.  110  shows  a  Biehle 
testing  machine  of  100,000  pounds  capacity,  as  installed  in  the 
laboratory.  It  is  of  the  automatic  and  autographic  type  and  is 
described  by  the  makers  as  follows : 

The  Straining  Mechanism. — The  top  head  is  supported  by  two 
cast-iron  columns,  which  rest  on  the  weighing  table.  This  table 
in  turn  rests  upon  a  series  of  eight  hardened  steel  knife  edges  in 
the  main  levers,  these  levers  resting  on  steels  which  are  fitted  in 
cast-iron  bearings  on  the  cover  plate.  Beneath  this  and  bolted  to 
it  is  the  cast-iron  box,  containing  the  main  gears,  and  to  which  the 
bracket  supporting  the  beam  and  lever  stands  is  attached. 

Through  holes  in  the  table  two  pulling  screws  pass  up  and  reach 
nearly  to  the  top  head,  running  through  two  brass  nuts  in  the  pull- 
ing head,  which  is  raised  or  lowered  according  to  which  direction 
the  screws  revolve.  In  the  top  head  and  pulling  head  are  cut  rec- 
tangular holes,  sloping  on  two  sides.  For  tensile  tests,  the  ends  of 
the  specimen  are  held  by  hardened  steel  wedges,  or  "  grips/'  which 
fit  into  these  openings  in  the  heads.  Owing  to  their  wedge  shape, 
the  grips  hold  the  specimen  more  firmly  as  the  strain  on  it  increases. 

In  compression  tests  the  specimen  is  crushed  between  the  two 
crushing  tools,  one  being  attached  to  the  under  side  of  the  pulling 
head,  and  the  other  resting  centrally  on  the  table. 

In  bending  tests,  one  V-shaped  tool  is  attached  to  the  lower 
side  of  the  pulling  head,  the  other  two  V-shaped  tools  resting  on  the 
table  equidistant  from  the  first,  and  as  far  from  it  as  the  operator 
wishes.  The  specimen  rests  on  the  two  tools  placed  on  the  table 
and  is  bent  or  broken  by  the  third  tool  pressing  down  upon  it.  In 
shearing  tests  a  similar  arrangement  is  used  except  that  in  place  of 
the  three  V-shaped  tools,  the  shearing  tool,  Fig.  Ill,  is  employed. 
The  block  which  carries  the  knives  and  specimen  rests  on  the  table 
of  the  testing  machine,  and  the  pulling  head,  carrying  a  crushing 
tool,  forces  the  upper  knife  through  the  specimen.  The  lower  block 
is  cast  iron,  with  a  V-groove,  in  which  the  specimen  is  placed.  The 
two  lower  knives  are  exactly  one  inch  apart  and  are  held  in  the  block 
with  a  wedge,  by  which  they  are  brought  to  the  correct  position. 
The  upper  knife,  which  is  movable  and  guided  by  the  block,  is  one 
inch  in  width  so  that  it  just  fills  the  space  between  the  two  lower 
knives,  as  it  is  forced  through  the  specimen. 


110. 


194 


EXPERIMENTAL  ENGINEERING 


The  table  is  kept  from  jumping  by  the  recoil  bolts  which  pass 
through  its  four  corners,  running  up  from  the  cover  plate,  and 
are  secured  by  nuts  with  thick  rubber  washers,  which  serve  to  take 
up  the  shock  occasioned  by  the  breaking  of  large  specimens. 

The  Weighing  Apparatus. — The  table  rests  wholly  upon  the 
main  levers,  the  recoil  bolts  passing  through  it  loosely,  and  any  pres- 
sure on  it  is  transmitted  directly  through  the  levers  to  the  beam. 
All  contacts,  by  which  the  load  is  transmitted  to  the  beam,  are  in  the 
form  of  hardened  steel  surfaces  resting  on  knife  edges,  by  which  the 
friction  is  eliminated.  A  heavy  weight  hanging  at  the  back  end  of 


RIEHLE 


,-  » 


FIG.  111. 


the  beam  serves  to  counterbalance  the  weight  of  the  other  end,  and 
a  counterpoise  above  this,  with  screw  and  hand  wheel  for  adjust- 
ment, permits  the  balancing  of  the  beam  when  the  poise  is  at  zero. 

When  making  a  test,  it  is  desirable  to  have  the  weight  registered 
on  the  beam  simultaneously  with  the  increase  of  the  load  on  the 
specimen,  the  equipoise  of  the  beam  being  maintained  as  nearly  as 
possible.  The  poise  should  be  first  placed  at  zero  and  the  beam  bal- 
anced, then  as  the  load  is  added  the  poise  should  be  advanced  at 
such  a  rate  that  the  beam  vibrates  freely  between  the  upper  and 
lower  bars  at  the  smaller  and  further  end.  The  load  on  the  speci- 
men is  only  weighed  accurately  when  the  beam  is  in  equipoise. 
When  the  beam  is  against  the  upper  bar  the  load  is  greater  than  the 


TESTING  MATERIALS  OF  CONSTRUCTION  195 

poise  indicates,,  and  it  is  impossible  to  know  just  how  much  greater 
until  the  beam  is  again  balanced  by  the  outward  movement  of  the 
poise. 

The  Screw  and  Vernier  Beams. — The  beam  is  graduated  in  1000 
pound  marks,  but  from  the  dial  at  the  operating  end  of  the  beam, 
subdivisions  of  100  pounds  and  10  pounds  can  be  read.  One  revo- 
lution of  the  screw  moves  the  poise  forward  1000  pounds. 

The  poise  is  attached  to  a  carriage  running  along  the  top  of  the 
beam  on  rollers,  and  is  propelled  by  a  screw  sunk  in  the  top  of  the 
beam.  The  screw  revolving,  carries  the  poise  out  or  back,  as  the 
case  may  be,  or  the  nut  can  be  released  from  the  screw  and  the  poise 
run  back  quickly  by  hand. 

The  Driving  Mechanism. — The  two  pulling  screws  pass  down 
through  long  bearings  in  the  cover  plate  and  to  their  lower  ends  are 
keyed  the  main  gear  wheels.  Between  these  gears  and  the  cover 
plate  are  ball  bearings  to  take  the  thrust  and  reduce  friction.  Both 
these  wheels  are  driven  by  the  same  pinion  on  a  vertical  shaft, 
which  is  driven  through  the  large  bevel  wheel  shown  in  cut.  This 
in  turn  is  driven  by  a  large  bevel  pinion,  which  receives  its  motion 
through  a  series  of  gears  from  the  pulley  shaft  down  in  cut.  As 
installed  in  the  laboratory,  this  pulley  is  driven  by  a  reversible  elec- 
tric motor. 

The  lever  to  right  of  pulley  throws  the  motor  in  direct  gear  for 
quick  speeds.  The  small  hand  wheel  to  left  of  pulley  throws  in  the 
back  gear,  which  can  only  be  operated  when  the  lever  is  vertical, 
disconnecting  the  direct  gear. 

The  lever  to  left  of  hand  wheel  operates  to  give  two  speeds,  and 
two  speeds  are  given  by  the  tumbling  ball  lever  at  base  of  machine. 
There  are  thus  seen  to  be  eight  speeds  for  the  pulling  head,  which, 
for  a  speed  of  200  revolutions  per  minute  for  the  pulley  shaft,  are 
as  follows : 

Speed  per  min.  B^ekGear.  Lever.  Tumbling  Ball. 

^  inch  Back  Slow  Slow 

£  inch  Back  Fast  Slow 

1.  inch  Back  Slow  Fast 

2  inch  Direct  Slow  Slow 

1|  inches  Back  Fast  Fast 

2  inches  Direct  Fast  Slow 

3  inches  Direct  Slow  Fast 
10    inches  Direct  Fast  Fast 


196  EXPERIMENTAL  ENGINEERING 

The  fastest  speed  is  used  only  for  adjustment  of  the  pulling  head 
to  the  desired  position.  If  speeds  slower  than  1/10  inch  are  de- 
sired, they  can  be  obtained  by  stopping  the  motor  and  operating 
the  pulley  shaft  by  hand. 

The  Automatic  Apparatus. — On  the  beam  stand  of  the  ma- 
chine is  the  attachment  for  operating  the  poise  automatically.  A 
small  belt  runs  from  the  hub  of  the  driving  pulley.  This  sheave 
turns  a  cast-iron  disc  which  is  arranged  to  give  motion  to  either  of 
a  pair  of  fiber-rimmed  wheels  placed  near  the  periphery,  on  oppo- 
site sides  of  the  disc.  These  wheels  are  on  the  same  spindle  which 
is  connected  by  a  belt  to  the  wheel  for  operating  beam  screw.  A  pair 
of  electro-magnets  are  so  placed  that  when  current  is  turned  on  one 
of  them,  an  armature  is  attracted  and  one  of  the  fiber-covered  wheels 
is  brought  against  disc.  With  current  on  the  other  magnet  the 
other  wheel  is  brought  in  contact.  The  end  of  beam  has  electrical 
contact  points,  arranged  so  that  when  the  beam  rises  the  circuit  is 
completed  that 'brings  the  wheel  into  action  for  forcing  the  poise 
outward.  When  the  beam  falls  this  contact  is  broken  and  the  poise 
remains  stationary  until  the  lower  electrical  contact  is  made  and  the 
other  wheel  is  brought  into  action,  forcing  the  poise  backward.  The 
fiber-covered  wheels  may  be  shifted  back  and  forth  across  the  face 
of  the  disc,  thus  giving  variation  to  the  speed  of  the  poise. 

The  Autographic  Apparatus. — The  extensometer  for  autographic- 
ally  recording  the  stretch  or  compression  of  a  specimen  is  shown 
attached  to  bracket  fixed  to  the  back  of  one  of  the  columns.  The 
arm  of  extensometer  carrying  fingers  is  swung  into  position  for 
test,  and  adjusted  vertically.  The  upper  finger  of  extensometer  is 
placed  under  top  spring  clamp.  The  lower  finger  rests  upon  bottom 
spring  clamp,  and  moves  with  it  as  specimen  stretches.  The  motion 
of  stretch  is  converted  into  circular  motion  and  transferred  by  gear- 
ing and  a  sliding  shaft  with  universal  joints  to  the  paper  drum 
attached  to  beam  stand  above  beam.  The  motion  as  transferred  to 
the  paper  is  multiplied  five  times.  A  vertical  screw  in  front  of  drum 
carries  the  pencil  attached  to  nut.  This  screw  has  a  finer  pitch  than 
beam  screw  to  reduce  load  line  on  diagram,  and  moves  simultane- 
ously with  the  beam  screw.  The  rotary  motion  of  drum,  due  to 
stretch  of  specimen,  and  the  vertical  movement  of  pencil,  due  to 
load,  form  the  strain  diagram. 


TESTING  MATERIALS  OF  CONSTRUCTION  197 

The  fingers  of  extensometer  should  be  swung  to  one  side  just 
before  the  specimen  breaks,  in  order  to  prevent  injury  to  the  in- 
strument. 

The  Riehle-Kenerson  Extensometer. — This  extensometer,  shown 
in  Fig.  112,,  was  designed  by  Prof.  Kenerson,  of  Brown  University, 
and  "is  arranged  to  draw  the  strain  diagram  of  a  tension  specimen 
to  just  beyond  the  elastic  limit  with  about  150  magnification,  per- 
mitting the  modulus  to  be  obtained  direct  from  the  diagram.  It 
can  also  be  used  as  a  micrometer  extensometer,  reading  to  .0001 
inch. 

The  instrument  is  attached  to  the  specimen  by  means  of  set 
screws,  three  in  the  upper  and  two  in  the  lower  clamp.  The  upper 
clamp  supports  the  mechanism  of  the  instrument,  including  the 
cylinder  on  which  the  diagram  sheet  is  placed,  the  weight  to  which 
the  pencil  is  attached,  and  the  micrometer  drums.  The  two  set 
screws  in  lower  clamp  are  placed  exactly  opposite  on  the  specimen 
so  as  to  suspend  this  clamp  between  them.  On  one  side  of  this 
clamp  is  a  column  with  pivot  and  screw  for  adjustment.  The  other 
side  supports  the  spindle  carrying  micrometer  drums.  This  spindle 
rests  on  a  pivot,  but  its  upper  end  is  threaded  and  passes  through 
a  nut  in  upper  clamp.  It  carries  a  grooved  drum,  around  which  is 
wound  a  cord  for  supporting  the  weight  to  which  pencil  is  attached. 
As  the  specimen  is  stretched  this  weight  descends  and  causes  the 
spindle  to  revolve  in  its  nut,  thus  indicating  the  amount  of  the 
extension  directly  on  the  graduated  wheel  and  vernier. 

A  cord  is  attached  to  the  poise  on  the  beam  of  the  testing  machine 
and  through  a  reducing  motion  turns  the  cylinder.  As  the  speci- 
men stretches  the  pencil  moves  downward  and  the  combined  move- 
ment produces  the  diagram.  The  diagram  card  is  6  inches  long 
by  5  inches  high,  and  with  a  magnification  of  150,  this  permits  a 
specimen  to  stretch  .03  inch.  When  used  as  a  micrometer  extenso- 
meter, a  stretch  of  1  inch  can  be  noted. 

This  instrument  produces  a  card  similar  to  that  made  by  the 
autographic  apparatus  on  the  testing  machine,  but  on  a  greatly  en- 
larged scale.  It  is  only  used  for  work  up  to  the  elastic  limit. 

Practical  Use  of  the  Testing  Machine. — In  all  specifications  for 
machinery,  the  material  is  required  to  meet  certain  requirements 


TESTING  MATERIALS  OF  CONSTRUCTION  199 

as  to  strength  and  elasticity.  One  or  more  test  pieces  must -be  cut 
from  every  heat,  to  be  tested  by  the  inspector  before  such  material 
can  be  passed.  It  is  usual  to  fix  the  minimum  requirements  as  to 
(1)  coefficient  of  ultimate  strength,  (2)  coefficient  of  strength  at 
the  elastic  limit,  (3)  percentage  of  elongation,  (4)  percentage  of 
reduction  of  area. 

The  usual  method  of  conducting  a  test  is,  after  balancing  th« 
beam  at  zero  load,  to  gradually  apply  the  load,  keeping  the  beam 
balanced  by  running  the  poise  out  by  hand.  At  the  yield  point,  the 
beam  suddenly  drops.  The  load  at  this  point  is  recorded  and  from 
it  the  coefficient  of  strength  at  the  elastic  limit  is  calculated.  The 
test  is  then  carried  on  to  the  breaking  point.  The  maximum  load  is 
thus  obtained  and  from  it  the  coefficient  of  ultimate  strength  is  cal- 
culated. The  specimen  is  then  removed  from  the  machine  and  the 
two  parts  having  been  put  together,  the  total  elongation  is  measured 
directly  and  the  diameter  at  the  break  taken.  From  these  the  per- 
centages of  elongation  and  reduction  of  area  are  calculated. 

If,  as  in  some  cages,  the  modulus  of  elasticity  is  also  required,  an 
extensometer  must  be  used  to  determine  the  amount  of  elongation 
at  the  elastic  limit. 

Test  Record. — 

Date: 

Specimen  of : Tested  in : 

Original  dimensions :    L— :  d= :  area= 

Final  dimensions :    L— :  d— :  area= 

(1)  Coefficient  of  strength  at  elastic  limits 

(2)  Coefficient  of  ultimate  strength  = 

(3)  Percentage  of  elongation  in  8  inches 

(4)  Percentage  of  reduction  of  area 

(5)  Modulus  of  elasticity   

(l\—       Load  at  elastic  limit 


(2)  = 


Original  area  of  specimen  ' 

Maximum  load 
Original  area  of  specimen  9 


i<*\  _  Final  length -original  length  v1ftn. 
Original  length  °J 


200  EXPERIMENTAL  ENGINEERING 

/  .v  _  Original  area  — final  area      -™ 
Original  area 


elongation  at  elastic  limit ' 

Compression  Tests. — Materials  are  tested  in  compression  to  de- 
termine their  crushing  strength  and  strength  to  resist  bending; 
also  at  times  their  elastic  limits,  and,  if  ductile,  their  plastic  limits. 
Short  specimens,  those  whose  length  is  less  than  five  diameters, 
usually  fail  by  crushing  or  flowing.  Long  specimens  usually  fail 
by  bending  toward  the  side  of  least  resistance. 

Materials  may  be  divided  into  two  general  classes,  in  accordance 
with  their  behavior  when  subjected,  in  short  specimens,  to  compres- 
sional stress.  In  the  first  classification  are  the  plastic  materials, 
such  as  wrought  iron,  soft  steel,  copper,  the  alloys,  etc.,  which  fail  by 
flowing.  After  the  elastic  limit  is  passed,  further  compression  re- 
sults in  an  increase  in  the  cross  sectional  area  under  a  continually 
increasing  load.  For  such  materials  there  are  two  fixed  points  inde- 
pendent of  shape  of  specimen,  viz.,  the  elastic  limit  and  the  plastic 
limit.  It  has  been  found  that  the  elastic  limit  of  these  materials  is 
nearly  the  same  as  their  elastic  limit  in  tension,  and  for  this  reason, 
and  in  view  of  the  difficulty  of  measuring  the  deformation  of  short 
specimens,  compressional  tests  upon  them  are  seldom  made. 

The  second  classification  embraces  the  brittle  materials,  such  as 
stone,  brick,  wood,  cement,  cast  iron,  etc.,  which  fail  by  crushing, 
due  to  the  shearing  on  definite  angles.  With  these  materials  the 
ultimate  strength  is  easily  determined. 

In  general  it  may  be  said  that  compressional  tests  are  very  rarely 
required  for  materials  used  in  naval  engineering.  For  soft  steel  and 
steel  of  high  grade  such  as  is  used  in  building  machinery  the  charac- 
ter of  the  material  is  sufficiently  well  determined  by  tensile  tests. 

Cross  Bending  Tests  are  used  to  determine,  in  case  of  brittle 
materials,  like  cast  iron,  the  modulus  of  rupture  and  the  resilience, 
and  in  ductile  materials  like  wrought  iron  and  soft  steel,  the  elastic 
limit  and  modulus  of  elasticity.  Other  tests  on  springs,  rails,  rail 
joints,  etc.,  determine  the  stiffness,  i.  e.,  the  deflection  at  given 
loads,  the  elastic  limit,  and  in  some  cases,  the  ultimate  strength. 


TESTING  MATERIALS  OF  CONSTRUCTION 


201 


For  naval  purposes,  cross  bending  tests  are  frequently  required 
on  cast  iron.  They  are  usually  limited  to  the  determination  of  the 
coefficient  of  ultimate  strength. 

Shearing  Tests  are  not  prescribed  in  the  Specifications  for  the 
Inspection  of  Engineering  Material  in  the  Navy.  If  the  tensile 
properties  of  a  metal  are  known,  or  can  be  ascertained,  it  is  suffi- 
cient for  all  practical  purposes  to  assume  the  shearing  strength  to 
bear  a  definite  ratio  to  the  tensile  strength.  This  applies  to  material 
under  a  direct  shear,  as  in  a  riveted  joint.  Shearing  also  takes  place 
in  a  bar  subjected  to  torsional  stress,  acting  in  a  rotary  direction 
around  the  axis.  Such  stresses  are  best  investigated  in  a  torsional 
testing  machine. 

DEPARTMENT  OF   MARINE   ENGINEERING   AND   NAVAL   CONSTRUC- 
TION,  U.  S.   NAVAL  ACADEMY. 

TESTS  OP  "ELEPHANT  BRAND"   PHOSPHOR  BRONZE,  MADE  WITH  THE  RIEHLE 

SCREW  POWER  TESTING  MACHINE.     BRANDS  A,  B,  S,  AND  F2, 

CAST  IN  GREEN  SAND.     BRANDS  X  AND  Y,  ROLLED. 


TENSION. 


Finished  rods. 


Original  length  inches  

2. 

2. 

2.358 
.977 
.875 
.75 
.601 
15,630 
24,360 
17.9 
19.87 
20,840 
32,480 

2. 

.965 
.965 
.732 
.732 

22,160 

o.o 
o.o 

30,273 

2- 
2.14 
.930 
.906 
.680 
.645 
18,160 
21,230 
7.0 
5.15 
26,706 
31,221 

2. 

2.718 
.798 
.437 
.5 
.15 
21,920 
35,700 
35.9 
70.0 
43,840 
71,400 

10. 
11.188 
.798 
.422 
.5 
.14 
21,522 
29,840 
11.88* 
72.0 
43,044 
59,680 

Final  length  inches       

....     2.45 

977 

844 

75 

.56 

Load  at  elastic  limit   Ibs 

...    14  680 

.  .  .    25  230 

.   ..  22  5 

.  .  95  3 

Coef  of  elastic  strength 

.  .  .  .   19  573 

...    33  640 

*  In  10  inches. 
Brand 

COMPRE 

ISSION. 

B                 F2 
Round       Square 
1.                 1. 
.622              .945 
.786            1. 
1.11              1.05 
37.8                5.5 
41.22               5.0 

S 
Round 
1. 
.655 
.786 
1.05 
34.5 
33.59 

S 
Square 
1. 
.745 
1. 
1.21 
25.5 
21.0 

Square 

687 

1 

..  .        1  41 

31  3 

Per  cent  increased  area.  .. 

41.0 

Specimens  were  still  within  the  plastic  limit  and  showed  no  signs  of  rupture 
under  a  load  of  100,000  pounds,  the  limiting  load  of  the  machine. 


202  EXPERIMENTAL  ENGINEERING 

Standard  Test  Pieces.    Bureau  of  Steam  Engineering  Standards. 

— The  specifications  for  steel  and  iron  prescribe  that  "  Test  pieces 
from  blooms,  rolled  bars,  forgings,  and  castings  are  to  have  a  length 
of  2  inches  between  measuring  points  and  an  area  of  cross  section 
of  0.2  square  inch,  diameter  0.505  inch."  Test  pieces  for  composi- 
tion castings  have  a  length  of  2  inches  between  measuring  points 
and  an  area  of  cross  section  of  1  square  inch. 

Full-size  bars  and  rods,  within  the  capacity  of  the  testing  ma- 
chine, may  be  used  as  tensile  test  pieces. 

Test  Pieces  from  Plates. — When  heats  are  rolled  into  plates  of 
varying  thickness,  the  test  pieces  shall  be  taken  from  plates  not  less 
than  0.3-inch  thick.  The  standard  width  of  tensile  test  pieces  from 
plates  and  boiler  tubes  will  be  1J  inches,  the  thickness  the  same  as 
the  plate  or  tube,  and  the  length  between  measuring  points  8  inches. 

All  tensile  test  pieces  shall  be  uniform  in  cross  section  between 
measuring  points.  A  variation  of  5%  above  or  below  in  area  is 
allowed. 

The  Bureau  of  Ordnance  uses  two  standard  test  pieces.  Fig.  113 
shows  the  standard  used  for  blooms,  forgings,  bars,  and  castings. 
Fig.  114  shows  the  standard  for  plate  material.  It  will  be  noted 
that  these  standards  also  meet  the  specifications  of  the  Bureau  of 
Steam  Engineering  for  most  material. 

Richie-Miller  Torsional  Testing  Machine. — This  machine,  shown 
in  Fig.  115,  consists  of  a  head  for  applying  the  stress  to  the  speci- 
men, and  a  carriage  for  carrying  the  weighing  mechanism  and 
the  head  which  receives  and  transmits  the  load  to  the  weighing 
mechanism.  The  twisting  head  is  operated  through  worm  gearing 
and  spur  gearing  to  reduce  the  motion  of  the  head.  The  worm  shaft 
is  connected  to  the  motor  by  a  silent  chain  drive.  The  motor  is 
reversed  by  a  controller  which,  by  means  of  resistance  box,  gives 
six  variations  of  speed  in  either  direction,  varying  from  50%  to 
the  normal  speed  of  the  motor.  There  is  a  lever,  seen  just  above 
spur  wheel  on  head,  for  operating  the  friction  clutch  to  start  or  stop 
the  machine.  The  weighing  end  can  be  adjusted  to  suit  different 
lengths  of  specimens  up  to  5  feet,  by  means  of  a  rack  and  pinion 
operated  by  hand  wheel. 

The  head  on  weighing  end  has  a  set  of  toggle  grips  for  holding 


TESTING  MATERIALS  OF  CONSTRUCTION 


203 


the  specimen,  and  is  supported  by  a  parallel  system  of  levers  that 
completely  neutralize  any  load  except  the  torsion  or  twisting  load 
exerted  on  the  specimen.  A  similar  grip  arrangement  holds  the 
other  end  of  specimen  in  the  head  that  applies  the  load.  These 
grips  are  designed  to  take  round  or  hexagon  specimens  from  J  inch 
to  1J  inches  in  diameter. 

The  beam  is  similar  to  that  for  the  testing  machine,  previously 
described,  but  the  poise  is  moved  by  hand  wheel  only. 


10  THREADS  PER   INCH 


FIG.  113. 


—  -s  --q-1%0- 

—  zy  •  — 

\ 

f.9 

o 

i      »      .      t     *" 

•J 

1 

Y 

-* 

J*PJ7£ 

Ift"                       +• 

OF  SAME  THICKNESS  ASTHE   PLATE 

FIG.  114. 

The  angle  of  torsion  of  the  specimen,  or  the  number  of  turns 
required  to  break  the  specimen,  is  noted  on  the  graduated  ring  at- 
tached to  the  twisting  head. 

The  Torsion  Indicator. — In  reading  the  angle  of  torsion  on  the 
head  of  the  machine,  it  is  difficult  to  eliminate  errors  due  to  the 
slipping  of  the  specimen  in  the  grips.  To  avoid  this  difficulty,  it  is 
necessary  to  use  an  indicator  attached  directly  to  the  specimen.  The 
one  in  use  in  the  laboratory  consists  of  a  disc,  graduated  on  its  outer 
edge  in  degrees,  clamped  on  one  end  of  the  specimen,  and  a  pointer 
clamped  on  the  other  end,  the  finger  of  the  pointer  extending  paral- 


204 


EXPERIMENTAL  ENGINEERING 


TESTING  MATERIALS  OF  CONSTRUCTION  205 

lei  to  the  specimen,  up  to  the  graduations  on  the  face  of  the  disc. 
The  movement  of  the  pointer  over  the  graduated  disc  indicates  the 
angle  of  torsion. 

With  this  form  of  indicator,  a  different  pointer  is  required  for 
each  length  of  specimen.  The  Eiehle  Torsion  Indicator  avoids  this 
difficulty  and  is  suitable  for  specimens  of  any  length.  A  light  gear 
wheel  is  attached  to  each  end  of  the  specimen  by  3  set  screws.  Each 
of  these  drives  a  pinion  moving  a  pointer  over  a  dial.  The  dial  is 
graduated  and  when  the  gear  wheel  is  turned,  the  angle  is  indicated 
to  within  ^  degree  on  the  dial.  With  a  specimen  under  test  the 
reading  of  both  dials  is  taken  and  the  reading  on  the  dial  near  the 
weighing  end  is  subtracted  from  the  reading  of  the  dial  near  the 
power  end. 

Cements. 

Cements  are  used  only  to  a  limited  extent  on  board  a  ship,  but 
their  use  is  so  extensive  in  other  branches  of  engineering  allied 
to  marine  engineering,  that  some  knowledge  of  them  and  the  method 
of  testing  them  is  of  importance  to  the  naval  engineer. 

Hydraulic  Cement  may  be  broadly  defined  as  a  material  which, 
when  pulverized  and  mixed  with  water  into  a  paste,  acquires  the 
property  of  setting  and  hardening  under  water.  In  engineering 
work,  four  classes  of  cement  are  generally  recognized — (1)  Portland 
cement,  (2)  natural  cement,  (3)  Pozzuolana  cement,  (4)  mixed  or 
blended  cement. 

Portland  Cement  is  an  artificial  cement,  manufactured  from 
selected  materials,  commonly  limestone  and  clay,  with  other  mate- 
rials varying  with  each  brand.  The  mixture  is  calcined  until  the 
materials  begin  to  run  together  and  the  resulting  clinker  is  ground 
to  a  fine  powder.  It  is  named  from  its  resemblance  in  color  to  the 
famous  Portland  limestone  in  England. 

Natural  Cement  is  the  product  resulting  from  the  burning  and 
subsequent  pulverization  of  an  impure  grade  of  limestone,  con- 
taining lime  and  clay,  the  heat  of  burning  being  insufficient  to  cause 
vitrefaction.  It  is  sometimes  called  Roman  cement,  from  a  fancied 
resemblance  to  Eoman  mortar.  In  the  United  States  it  is  also 
widely  known  as  Eosendale  cement,  from  the  town  in  the  State  of 
New  York,  where  much  of  it  is  produced. 


206  EXPERIMENTAL  ENGINEERING 

Pozzuolana  or  Puzzolan  Cement  is  obtained  by  grinding  together 
an  intimate  mixture  of  slaked  lime  and  blast  furnace  slag  or  vol- 
canic lava.  It  is  not  burned,  the  hydraulic  ingredients  being  present 
only  as  a  mechanical  mixture.  It  is  so  named  from  a  town  in  Italy 
where  much  of  it  is  made  and  where  there  is  a  large  deposit  of  the 
particular  form  of  lava  used. 

Mixed  Cements  cover  a  large  variety  of  products,  made  by  com- 
bining the  other  forms  of  cement,  or  mixing  them  with  an  inert 
material.  "  Improved  Cements  "  are  naturals,  containing  from  10 
to  30  per  cent  of  Portland  clinker.  Sand  cements  are  made  by  finely 
grinding  a  mixture  of  Portland  cement  and  sand  in  varying  propor- 
tions dependent  upon  the  use  to  which  they  are  to  be  applied. 

Neat  Cement  is  cement  mixed  with  water  only. 

Concrete  is  a  mixture  of  cement  with  sand,  stone,  or  pebbles,  and 
water. 

Reenforced  Concrete  contains  steel  bars  or  other  shapes  to  give 
added  strength. 

Portland  cement  is  the  variety  commonly  employed  and  when 
the  term  cement  is  used  without  qualification,  this  is  what  is  gen- 
erally understood.  The  commercial  article  is  usually  a  mixture 
containing  more  or  less  sand.  For  this  reason  the  specifications  for 
cement  are  closely  drawn  in  order  to  obtain  material  of  the  quality 
desired.  In  ordinary  use,  one  part  is  mixed  with  from  -J  to  5  parts 
of  sand  according  to  the  purpose  for  which  it  is  to  be  employed. 
The  cleaner  and  sharper  the  sand,  the  stronger  will  be  the  resulting 
mixture. 

Natural  cement  is  distinguished  in  use  by  its  lighter  weight, 
quicker  set,  and  lower  strength  in  the  earlier  stages  of  hardening. 
It  is  not  adapted  for  use  on  board  ship  on  account  of  its  lower 
strength. 

Salt  water  should  never  be  used  in  mixing  cement,  on  account  of 
the  action  of  the  salt  in  producing  disintegration. 

TJses  of  Cement  on  Board  Ship. — On  board  a  naval  vessel,  the 
bilges  and  double  bottoms  are  covered  with  cement  to  protect  the 
plating  and  make  them  easier  to  keep  clean.  Inaccessible  pockets 
in  bilges  are  frequently  filled  with  cement.  The  mixture  used  is  1 
part  best  Portland  cement  to  2  parts  sand. 


TESTING  MATERIALS  OF  CONSTRUCTION  207 

The  walls  of  trimming  tanks  and  tanks  for  the  storage  of  fresh 
water  are  covered  with  cement  to  prevent  corrosion.  For  this  pur- 
pose a  thin  wash  of  neat  cement  is  applied  with  a  paint  brush. 

In  old  boilers,  with  leaky  shell  seams  that  give  trouble,,  cement 
is  sometimes  used  to  advantage.  When  thus  used  the  surfaces 
must  be  quite  clean  and  the  cement  in  the  form  of  a  thin  wash, 
mixed  neat,  is  applied  on  the  inside  of  the  boiler.  Considerable  care 
must  be  exercised  in  order  to  stop  a  leak  by  this  method,  as  water 
will  in  many  cases  work  its  way  along  the  seam  from  a  point  some 
distance  removed  from  the  leak.  When  thus  used  on  a  steel  or  iron 
surface  exposed  to  heat,  but  little  trouble  is  experienced  with  the 
cement  cracking,  since  its  coefficient  of  expansion  is  approximately 
the  same  as  that  of  the  metal. 

Cement  Testing. — The  usual  tests  applied  to  cement  are  those  for 
specific  gravity,  tensile  strength,  fineness,  constancy  of  volume,  and 
time  of  initial  and  final  set.  It  is  not  usual  to  make  compression 
tests  in  America.  The  results  in  tension  vary  directly  with  those  in 
compression,  so  that  the  tensile  strength  is  a  satisfactory  index  of 
the  value  of  the  cement  in  compression. 

The  Standard  Cement  Specifications  of  the  American  Society  for 
Testing  Materials  provide  that  the  acceptance  or  rejection  of  cement 
shall  be  based  on  the  following  requirements : 

Specific  Gravity.— The  specific  gravity  of  the  cement  thoroughly  dried 
at  100°  C.,  shall  be  for  Portland  cement  not  less  than  3.10,  and  for 
natural  cement  not  less  than  2.8. 

Fineness. — Portland  cement  shall  leave  by  weight  a  residue  of  not 
more  than  8#  on  the  No.  100  and  25$  on  the  No.  200  sieve.  Natural 
cement  shall  leave  not  more  than  10#  on  the  No.  100  and  30#  on  the 
No.  200  sieve. 

Time  of  Setting. — Portland  cement  shall  develop  initial  set  in  not 
less  than  30  minutes  and  final  or  hard  set  in  not  less  than  one  hour 
nor  more  than  10  hours.  Natural  cement  shall  develop  initial  set  in 
not  less  than  10  minutes  and  hard  set  in  not  less  than  30  minutes  nor 
more  than  3  hours.  Setting  of  the  samples  under  test  should  take  place 
in  moist  air  under  as  uniform  conditions  as  possible.  A  sudden  change 
or  range  of  temperature  in  the  room  in  which  the  tests  are  made,  a 
very  dry  or  humid  atmosphere,  and  other  irregularities,  vitally  affect 
the  rate  of  setting. 

Tensile  Strength. — The  minimum  requirements  for  tensile  strength 
for  briquettes  one  inch  square  in  cross  section  shall  be  within  the 


208  EXPERIMENTAL  ENGINEERING 

following  limits,  and  shall  show  no  retrogression   in  strength  within 
the  periods  specified:  * 

Portland  Cement,  Neat. 

Strength. 
Lbs. 

24  hours  in  moist  air 150-200  * 

7  days,  1  day  in  moist  air,  6  days  in  water. . .  450-550 
28  days,  1  day  in  moist  air,  27  days  in  water. .   550-650 

One  Part  Portland,  Cement,  Three  Parts  Standard  Sand. 
1  days,  1  day  in  moist  air,  6  days  in  water. .  150-200 
28  days,  1  day  in  moist  air,  27  days  in  water . .  200-300 

Natural  Cement,  Neat. 

Strength. 
Lbs. 

24  hours   in   moist  air 50-100 

7  days,  1  day  in  moist  air,  6  days  in  water..  100-200 
28  days,  1  day  in  moist  air,  27  days  in  water. .  200-300 

One  Part  Natural  Cement,   Two  Parts  Standard  Sand. 

1  days,  1  day  in  moist  air,  6  days  in  water. .     25-  75 

28  days,  1  day  in  moist  air,  27  days  in  water. .     75-150 

Constancy  of  Volume. — Pats  of  neat  cement  about  3  inches  in  diameter, 
y2  inch  thick  at  center,  tapering  to  a  thin  edge,  shall  be  kept  in  moist 
air  for  a  period  of  24  hours. 

(a)  A  pat  is  then  kept  in  air  at  normal  temperature  and"  observed 
at  intervals  for  at  least  28  days. 

(b)  Another  pat  is  kept  in  water  maintained  as  near  70°  Fah.,  as 
practicable,  and  observed  at  intervals  for  at  least  28  days. 

(c)  In  the  test  of  Portland  cement  only,  a  third  pat  is  exposed  in 
any  convenient  way  in  an  atmosphere  of  steam  above  boiling  water, 
in  a  loosely  closed  vessel  for  five  hours. 

These  pats,  to  satisfactorily  pass  the  requirements,  shall  remain 
firm  and  hard  and  show  no  signs  of  distortion,  checking,  cracking,  or 
disintegrating. 

Gilmore  Needles. — The  times  for  initial  and  hard  set  are  made 
respectively  with  a  needle  1/12  inch  in  diameter,  weighted  to  %  lb., 
and  1/24  inch  in  diameter,  weighted  to  1  Ib.  The  moment  when  the 

*  For  example,  the  minimum  requirement  should  be  some  specified 
value  within  the  limits  of  150  and  200  Ibs.,  and  so  on  for  each  period 
stated. 


TESTING  MATERIALS  OF  CONSTRUCTION 


209 


coarse  needle  fails  to  sink  into  the  cement,  when  held  lightly  in  a 
vertical  position  between  the  fingers,  the  point  resting  upon  the  speci- 
men, is  called  the  time  of  initial  setting,  and  similarly,  the  time  when 
the  fine  needle  will  no  longer  penetrate,  is  the  moment  of  final  or  hard 
setting. 

Tensile  Tests. — Fig.  116  shows  the  standard  form  of  tensile 
briquette  in  use  in  the  United  States.  It  is  1  inch  thick,  giving  an 
area  of  cross  section  of  1  square  inch  at  the  smallest  part  where  the 
break  occurs. 


/  \ 

/  \ 

/  \  J 

L  /  \    / 

I     / 


FIG.  116. 

The  samples  to  be  tested  are  thoroughly  mixed  and  the  specified 
quantity  of  water  added.  The  mixture  is  then  worked  up  into  a 
plastic  mass  and  moulded  in  brass  briquette  moulds.  It  is  usual  to 
do  this  work  by  hand  where  many  specimens  are  to  be  tested,  the 
experience  of  the  operator  giving  uniformity  of  results.  A  briquette 
making  machine  is  shown  in  Fig.  117,,  in  which  a  hammer  of  fixed 
weight  is  made  to  fall  on  a  disc  placed  over  the  mould  containing 
the  briquette.  The  number  of  strokes  is  fixed  and  the  blows  are 
stopped  automatically  after  a  definite  number.  The  machine  is 
useful  to  secure  briquettes  of  uniform  density  particularly  where 
but  few  tests  are  made  and  the  work  is  divided  among  several 
operators. 
14 


210 


EXPERIMENTAL  ENGINEERING 


Fairbanks'  Improved  Cement  Testing  Machine. — The  construc- 
tion of  this  machine  is  shown  in  Fig.  118.  Its  operation  is  de- 
scribed as  follows : 

Hang  the  cup  F  on  the  end  of  the  beam  D.  See  that  the  poise  R 
is  at  the  zero  mark  and  balance  the  beam  by  turning  the  ball  L.  Fill 
the  hopper  B  with  fine  shot.  Place  the  briquette  in  the  clamps 
N-N,  using  great  care  to  avoid  eccentricity.  Tighten  the  hand  wheel 
P  until  the  indicators  are  in  line.  By  means  of  the  hook  lever  Y 
the  worm  is  now  engaged  with  the  gear.  The  shot  valve  is  then 


FIG.  117. 

opened,  allowing  the  shot  to  run  into  the  bucket,  and  the  crank  is 
turned  with  sufficient  speed  to  hold  the  beam  in  equilibrium  until 
the  briquette  is  broken.  At  the  point  where  the  spout  joins  the  res- 
ervoir will  be  noticed  a  small  valve,  by  which  the  flow  of  shot  may 
be  regulated. 

When  the  briquette  breaks,  the  beam  D  will  drop  and  automati- 
cally close  the  valve  J.  Then  remove  the  cup,  with  its  contents, 
hanging  the  counterpoise  G  in  its  place.  Hang  the  cup  F  on  the 
hook  under  the  large  ball  E,  and  weigh  the  shot,  using  the  poise  R 
on  the  graduated  beam  D  and  the  weights  H  on  the  counterpoise  G 
The  result  will  give  the  number  of  pounds  required  to  break  the 
specimen. 


TESTING  MATERIALS  OF  CONSTRUCTION  211 


FIG.  118. 


CHAPTER  IX. 
ENGINE  LUBRICATION. 

Open  Systems. — Until  recently  all  engine  bearings  were  lubri- 
cated by  gravity  through  tubes,  the  oil  being  fed  into  the  tubes 
through  wicks.  Many  engines  built  in  the  last  few  years  have  been 
fitted  with  the  sight  feed  system,  in  which  the  flow  of  oil  to  each 
tube  is  regulated  by  a  valve,  a  portion  of  the  tube  being  made  of 
glass  to  permit  visual  regulation  of  the  flow. 

Much  attention  has  been  given  recently  in  our  navy  to  economy 
in  the  consumption  of  all  expendable  stores,  including  oil.  One  of 
the  results  has  been  to  direct  attention  to  the  superiority  of  the 
wick  feed  system.  By  varying  the  number  of  strands  in  the  wick 
and  the  number  of  wicks,  the  quantity  of  oil  can  be  regulated  to  a 
nicety.  Sight  feed  lubrication  cannot  be  closely  regulated  except 
by  the  most  careful  attention  which  it  is  difficult  to  give  where 
there  are  a  large  number  of  bearings  and  impossible  in  many  out 
of  the  way  locations. 

Forced  Lubrication. — In  late  machinery  designs  forced  lubrica- 
tion has  been  fitted.  The  oil  is  sent  to  the  bearings  under  pressure 
from  a  pump.  It  then  drains  to  a  receptacle  in  the  crank  pit  or 
elsewhere  low  down  in  the  ship,  where  it  is  taken  up  by  the  pump 
suction.  At  a  convenient  location  in  the  system  it  passes  through 
a  cooler  built  on  the  plan  of  a  surface  condenser,  where  the  heat 
from  the  bearings  is  given  up  to  the  cooling  water. 

This  system  permits  the  same  oil  to  be  used  over  and  over  again, 
the  only  new  oil  required  being  such  as  is  necessary  to  make  up 
losses  from  leakage  and  from  wear.  It  is  necessary  from  time  to 
time  to  pump  the  oil  into  tanks  and  allow  the  water  and  sediment 
to  settle,  thus  removing  it  from  the  system,  but  this  can  be  done  at 
such  times  as  will  not  interfere  with  the  operation  of  the  engines. 
This  system  is  very  economical  in  the  consumption  of  oil,  but  a 
greater  advantage  is  the  great  reduction  in  friction  and  wear  in 
the  bearings. 


ENGINE  LUBRICATION  213 

Engine  Lubricants. 

Practically  all  oils  used  for  lubricating  purposes  at  the  present 
time  in  the  United  States  have  as  their  base  a  heavy  mineral  oil, 
which  is  the  last  of  the  series  of  distillates  from  crude  petroleum. 
Various  other  constituents  are  added  by  oil  manufacturers  to 
obtain  a  compounded  oil  that  will  suit  the  particular  requirements 
for  which  it  is  intended.  The  oils  that  are  used  on  board  ship 
are  as  follows : 

Oils  for  Wick  or  Gravity  Feed. — These  are  compounded  oils  of 
high  lubricating  value  sufficiently  fluid  to  feed  well  through  wicks. 
Such  oils  are  usually  purchased  under  their  trade  names,  the  name 
carrying  the  manufacturers'  guarantee  of  the  good  quality  and  uni- 
formity of  the  oil.  Oils  of  this  character,  however  excellent  the  re- 
sults they  may  give  individually  are  not  likely  to  do  well  when  two 
or  more  brands  are  mixed.  When  changing  from  one  brand  to 
another  all  oil  cups  and  other  receptacles  must  be  thoroughly 
cleaned  before  starting  the  new  oil. 

These  oils  are  used  on  engine  pins  and  bearings  where  the  feed 
is  by  gravity.  Also  in  receptacles  such  as  thrust  bearings  where  the 
shaft  runs  in  a  bath  of  oil.  In  such  bearings  the  oil  usually  shows 
a  tendency  to  form  a  lather,  this  being  characteristic  of  mixed  oils 
where  any  water  is  present.  This  lather  is  itself  an  excellent  lubri- 
cant and  as  it  cannot  form  in  a  hot  bearing  its  presence  indicates 
that  the  bearing  is  working  well. 

Oils  for  Forced  Lubrication  must  be  pure  mineral  oils  on  account 
of  the  tendency  of  mixed  oils  to  lather  and  choke  the  small  pipes 
and  passages.  Such  oils  are  also  sold  under  trade  names  that  are 
accepted  as  guarantees  of  their  uniform  character.  Although  all 
such  oils  are  supposed  to  be  pure  mineral  oils,  it  will  be  found  the 
best  policy  not  to  begin  to  use  a  different  brand  without  first  clean- 
ing out  the  system. 

Cylinder  Oils  must  not  vaporize  or  carbonize  at  temperatures 
that  obtain  in  the  engine  cylinders.  They  must  therefore  have  a 
high  flash  point.  When  used  in  the  cylinders  a  considerable  per- 
centage passes  over  into  the  condensers  and  thence  into  the  boilers. 
In  order  to  produce  the  minimum  amount  of  injury  to  the  boilers 
thev  must  contain  no  acid.  These  conditions  are  best  met  in  a 


214  EXPERIMENTAL  ENGINEERING 

heavy  mineral  oil  with  no  animal  or  vegetable  constituents  and  it 
is  usual  to  specify  that  cylinder  oils  must  be  pure  mineral  oils. 

Cylinder  oil  was  considered  necessary  with  horizontal  engines. 
On  account  of  the  injury  to  boilers  and  particularly  to  water-tube 
boilers,  resulting  from  carrying  it  over  into  condensers,  it  became 
necessary  to  reduce  the  quantity  as  much  as  possible.  It  has  been 
found  practicable  to  entirely  dispense  with  it  in  vertical  engines, 
and  the  only  cylinder  oil  now  employed  is  used  to  swab  on  piston 
rods  in  case  they  should  run  warm  in  stuffing  boxes. 

Ice  Machine  Oils  must  not  vaporize  at  the  temperatures  that 
exist  in  the  compressor  cylinders.  Otherwise  the  oil  vapors  would 
pass  over  and  condense  in  the  pipes  of  the  system,  thus  preventing 
its  efficient  operation.  On  the  other  hand  in  a  machine  of  the  cold- 
air  type  the  same  oil  used  as  a  lubricant  for  the  expander  cylinder 
must  not  solidify  at  the  low  temperatures  existing  in  that  cylinder. 
A  cylinder  oil  might  be  satisfactory  in  the  compressor  cylinder  of 
a  compression  machine,  but  if  used  in  the  expander  cylinder  of  an 
air  machine  would  be  wholly  unsatisfactory.  It  is  best  when  prac- 
ticable to  obtain  ice  machine  oils  of  a  brand  that  is  known  to  be 
satisfactory. 

Vaseline,  etc. — Heavy  refined  petroleum  is  used  for  coating  pol- 
ished surfaces  that  are  liable  to  rust  when  not  in  use.  Engine 
cylinders  when  they  are  to  stand  idle  for  several  days  must  be 
wiped  out  and  coated  in  this  manner. 

Grease  cups  are  little  used  for  engine  lubrication  at  the  present 
time.  They  are  still  fitted  on  hoisting  and  other  machinery  subject 
to  irregular  use,  where  when  the  bearing  begins  to  warm  the  grease 
melts  and  runs  down.  Vaseline  may  be  used  in  grease  cups.  Albany 
grease  is  a  proprietary  preparation  usually  supplied  for  this  purpose. 
Tallow,  which  was  formerly  employed,  is  but  little  used  at  present 
on  account  of  the  acid  which  it  is  very  liable  to  contain  attacking 
the  polished  surface  of  the  pins. 

Testing  of  Lubricants. 

Determinations  Required. — The  following  particulars  are  re- 
quired in  a  complete  test  of  a  lubricant,  as  made  in  a  laboratory : 


ENGINE  LUBRICATION  215 

(1)  Its  composition,  including  the  detection  of  any  adulterant 
that  may  be  present. 

(2)  Its  specific  gravity. 

(3)  Its  viscosity. 

(4)  Any  tendency  to  gum. 

(5)  The  temperatures  of  flashing,  ignition,  and  solidification. 

(6)  The  detection  of  any  acid  that  it  may  contain. 

(7)  The  coefficient  of  friction. 

(8)  Its  durability  and  heat  removing  power. 

(9)  The  presence  of  any  grit  or  other  foreign  matter. 

The  composition  and  adulteration  of  a  lubricant  can  only  be 
properly  determined  by  a  chemical  analysis. 

The  specific  gravity  is  determined  by  the  ordinary  methods  in 
use  in  the  physical  laboratory.  Special  care  should  be  observed  to 
thoroughly  clean  all  instruments  with  benzine  after  using  for  the 
testing  of  oil. 

Viscosity  of  oil  is  closely  related  but  not  proportional  to  its 
density.  It  is  also  closely  related,  and  in  many  cases  inversely  pro- 
portional, to  its  lubricating  properties.  The  viscosity  varies  accord- 
ing to  the  temperature,  but  not  in  the  same  proportion  for  different 
oils,  hence  tests  for  viscosity  should  be  made  with  the  temperatures 
the  same  as  those  at  which  the  oil  is  to  be  used.  The  less  the  vis- 
cosity,  consistent  with  the  pressure  to  be  used,  the  less  the  friction 

The  viscosity  test  is  considered  of  great  value  in  determining  the 
lubricating  qualities  of  oils.  By  it  alone  we  could  probably  deter- 
mine the  lubricating  qualities  to  such  an  extent  that  a  good  oil  need 
not  be  rejected  nor  a  bad  oil  accepted.  There  are,  however,  no  set 
standards  for  the  determination  of  viscosity  and  the  results  are  to 
be  considered  as  comparative  rather  than  absolute. 

There  are  several  methods  of  determining  the  viscosity.  It  is 
usual  to  take  the  viscosity  as  inversely  proportional  to  the  flow 
through  a  standard  nozzle,  while  maintained  at  a  constant,  or  con- 
stantly diminishing  head,  and  constant  temperature.  A  comparison 
is  made  with  water  or  with  some  well-known  oil,  as  sperm,  lard,  or 
rape-seed,  taken  as  a  standard,  under  the  same  conditions  of  pres- 
sure and  temperature. 


216 


EXPERIMENTAL  ENGINEERING 


Engler's  Viscosimeter. — Engler's  Viscosimeter,  shown  in  Fig. 
119,  consists  of  a  chamber  holding  the  oil  to  be  tested,  a  water  bath, 
a  flask  graduated  so  as  to  receive  200  cc.  of  the  oil,  thermometers 
and  the  opening  through  which  the  heated  oil  flows  out  upon  the 
withdrawal  of  the  plug. 


FIG.  119. 

In  using  this  instrument  the  viscosity  of  an  oil  is  stated  in 
seconds  required  for  200  cc.  of  the  oil  to  run  into  the  flask.  Heat 
can  be  applied  to  the  water  bath,  the  viscosity  being  determined  at 
any  temperature  required  up  to  100°  C.  Any  temperature  up  to 
360°  C.  can  be  secured  by  filling  the  water  bath  with  paraffine 
instead  of  water. 

Engler  recommends  that  all  viscosities  be  compared  with  water, 
thus:  If  water  requires  fifty-two  (52)  seconds  for  delivery  of 
200  cc.  into  the  receiving  flask,  and  the  same  amount  of  an  oil 


ENGINE  LUBRICATION  217 

under  examination  requires  130  seconds,  the  ratio  is  determined  by 

130 

— —  =2.50,  the  oil  thus  having  a  viscosity  of  2.5  times  that  of 
o2i 

water. 

The  bath  is  filled  with  a  suitable  liquid  to  a  height  roughly  cor- 
responding with  the  point  of  the  gage  in  the  oil  cylinder.  Water 
answers  well  for  temperatures  up  to  90°  C.  or  200°  F.,  and  for 
higher  temperatures  a  heavy  mineral  oil  may  be  used.  The  liquid 
having  been  brought  to  the  required  temperature,  the  oil  to  be 
tested,  previously  brought  to  the  same  temperature,  is  poured  into 
the  cylinder,  until  the  level  of  the  liquid  just  reaches  the  point  of 
the  gage.  A  narrow-necked  flask  holding  200  cc.  to  a  point  marked 
on  the  neck,  is  placed  beneath  the  jet  in  a  vessel  containing  a  liquid 
of  the  same  temperature  as  the  oil.  The  rod  valve  is  then  raised,  a 
stop-watch  at  the  same  time  started,  and  the  number  of  seconds 
occupied  in  the  outflow  of  200  cc.  noted. 

It  is  of  the  greatest  importance  that  the  oil  cylinder  should  be 
filled  exactly  to  the  point  of  the  gage,  after  inserting  the  ther- 
mometer, and  that  the  standard  temperature  should  be  precisely 
maintained  during  the  experiment,  a  difference  of  -J  degree  F. 
making  an  appreciable  alteration  in  the  viscosity  of  some  oils. 
It  is  also  essential  that  the  oil  should  be  quite  free  from  dirt  or 
other  suspended  matter,  and  from  globules  of  water,  as  the  jet 
may  be  otherwise  partially  obstructed.  If  the  oil  cylinder  requires 
to  be  wiped  out,  paper  rather  than  cloth  should  be  employed,  as 
filaments  of  the  latter  may  be  left  adhering.  When  oils  are  being 
tested  at  temperatures  much  above  that  of  the  laboratory,  a  gas 
flame  is  applied  to  the  copper  heating  tube,  and  the  agitator  kept 
in  gentle  motion  throughout  the  experiment. 

The  Boverton-Redwood  Viscosimeter. — This  is  shown  in  Fig.  120. 
A  is  a  central  vessel  containing  the  oil  which  flows  out  through 
the  standard  orifice  at  B.  C  is  an  enveloping  vessel  around  A, 
through  which  hot  water  is  circulated,  passing  out  at  the  cock  D. 
E  is  a  framework  carrying  vanes  for  circulating  the  water  and  a 
thermometer  F  for  measuring  its  temperature.  G  is  a  thermometer 
for  measuring  the  temperature  of  the  oil.  H  is  a  handle  for  moving 
the  framework  E.  J  is  a  water  leg  to  which  a  lamp  is  applied  in 


218 


EXPERIMENTAL  ENGINEERING 


heating  up  the  oil.  K-K  are  thumb  screws  in  the  feet  of  the  sup- 
porting tripod,  by  which  the  instrument  is  levelled.  L  is  a  spirit 
level  which  is  placed  over  A  and  the  apparatus  levelled  by  its  guid- 
ance before  operations  are  commenced. 


FIG.  120. 


In  operation  the  standard  quantity  of  oil  is  placed  in  A  and 
brought  to  the  standard  temperature.  The  orifice,  which  has  been 
plugged,  is  then  opened  and  the  time  required  for  the  oil  to  flow 
through  is  noted. 


ENGINE  LUBRICATION  219 

Gumming  or  Drying  is  a  conversion  of  the  oil  into  a  resin  by 
oxidation,  and  occurs  on  exposure  of  the  oil  to  the  air.  In  linseed 
and  the  drying  oils  it  occurs  very  rapidly,  and  in  the  mineral  oils 
very  slowly. 

The  usual  method  of  testing  for  this  property  is  by  use  of  a 
slightly  inclined  plane  of  metal  or  glass.  A  small,  but  fixed,  quan- 
tity of  the  oil  is  started  at  the  upper  edge  of  the  plane  and  the  time 
required  to  reach  the  bottom  is  taken  as  a  measure  of  its  gumming 
properties.  Comparison  is  made  with  a  standard  oil.  This  test 
has  but  little  value  in  determining  the  quality  of  an  oil. 

A  better  test  is  made  with  the  standard  oil  testing  machine. 
Fresh  oil  is  applied,  a  run  made,  and  the  friction  noted.  After  the 
bearing  has  been  exposed  to  the  air  for  a  time,  a  second  run  is  made, 
and  the  increase  of  friction  is  noted.  In  this  case  also,  comparison 
must  be  made  with  some  standard  oil. 

The  Flash  Test. — The  effect  of  heat  is  to  increase  the  fluidity 
of  oils  and  to  lessen  the  viscosity.  The  temperature  at  which  oils 
flash,  ignite,  boil,  or  congeal  is  often  of  importance  in  the  determi- 
nation of  the  suitability  of  an  oil  for  some  special  purpose. 

The  temperature  at  which  inflammable  vapors  are  given  off  is  the 
flashing  point,  and  should  in  all  cases  be  known  for  inflammable 
oils  that  are  to  be  stored  on  board  ship.  The  test  is  made  in  two 
ways. 

The  Open  Cup. — The  oil  to  be  tested  is  placed  in  an  open  cup 
of  watch  glass  form,  which  rests  on  a  sand  or  water  bath.  Heat 
is  applied  to  the  bath-  and  as  the  oil  becomes  heated  a  lighted  match 
is  passed  at  intervals  of  a  few  seconds  over  the  surface  of  the  oil,  at 
a  distance  of  about  half  an  inch  from  it.  At  the  instant  of  flashing, 
the  temperature  of  the  bath  is  noted,  which  is  the  "  flash  point." 

Improvised  apparatus,  such  as  this,  is  sometimes  employed  for 
tests,  where  standard  instruments  cannot  be  obtained.  The  results 
are  subject  to  considerable  variation,  due  to  differences  in  the 
method  of  applying  the  match. 

The  New  York  State  Board  of  Health  Flash  Tester.— This  is 
shown  in  Fig.  121  and  is  on  the  open  cup  principle.  A  light  mica 
cover  rests  on  the  cup,  having  two  openings,  one  for  the  passage  of  a 
thermometer,  and  the  other  for  the  application  of  the  match.  While 


220 


EXPERIMENTAL  ENGINEERING 


not  sufficiently  heavy  to  confine  the  vapors,  this  cover  serves  to  give 
uniformity  to  the  results  obtained.  The  thermometer  in  the  oil 
measures  its  temperature  directly. 

The  Cleveland  Flash  Point  Tester. — Fig.  122  shows  the  Cleve- 
land Flash  Point  Tester.    The  oil  is  contained  in  a  central  vessel, 


FIG.  121. 

which  is  surrounded  by  a  bath  of  steam.  The  oil  is  completely 
covered  and  the  vapors  that  are  given  off  pass  down  through  a 
central  tube,  to  the  mouth  of  which  the  match  is  applied.  A  ther- 
mometer in  the  oil  gives  the  temperature  of  flashing.  A  second 
thermometer  in  the  surrounding  jacket  gives  the  temperature  of 
the  bath.  If  the  temperature  of  flashing  is  above  that  obtainable 
with  steam,  the  jacket  may  be  filled  with  sand  and  heated  by  the 


ENGINE  LUBRICATION 


221 


application  of  a  Bunsen  burner.  For  ordinary  purposes,  steam  is 
better,  since  the  heat  thus  obtained  is  more  uniform.  This  appara- 
tus is  largely  used  for  making  determinations  for  heavy  oils. 

Other    apparatus    for    making   the    flash    test    is    described    in 
Chapter  X. 


E- 


FIG.  122. 

The  Burning  Point  is  determined  by  heating  the  oil  to  such  a 
temperature,  that  when  the  match  is  applied  as  for  the  flash  test, 
the  whole  of  the  oil  will  take  fire.  The  reading  of  the  thermometer 
just  before  the  match  is  applied  is  the  burning  point.  The  appara- 
tus used  is  the  open  cup  flash  point  testing  apparatus  with  ther- 
mometer directly  in  the  oil  to  be  tested. 


222  EXPERIMENTAL  ENGINEERING 

Evaporation.— Mineral  oil  will  lose  weight  by  evaporation,  which 
may  be  determined  by  placing  a  given  weight  in  a  watch  glass 
and  exposing  to  the  heat  of  a  water  bath  for  a  given  time,  as  twelve 
hours.  The  loss  denotes  the  existence  of  volatile  vapors,  and  should 
not  exceed  5  per  cent  in  good  oil.  Other  oils  often  gain  weight 
under  these  conditions  by  the  absorption  of  oxygen. 

Cold  Tests  are  made  to  determine  the  behavior  of  oils  and  greases 
at  low  temperatures.  The  sample  to  be  tested  is  placed  in  a  test 
tube,  in  which  is  inserted  a  thermometer.  The  tube  is  then  packed 
in  a  freezing  mixture,  composed  of  small  particles  of  ice  mixed 
with  salt,  with  provision  for  draining  off  the  water.  After  the 
sample  has  congealed,  the  tube  is  removed  from  the  freezing  mix- 
ture, and  the  oil  is  stirred  gently  with  the  thermometer.  The 
temperature  indicated  when  the  oil  is  melting  is  the  chill  point. 

Acid  Tests. — The  ordinary  test  for  the  presence  of  acid  is  to 
observe  the  effect  on  blue  litmus  paper.  This  is  a  qualitative  test 
only,  and  is  not  very  satisfactory.  For  this  test  a  sample  of  the  oil 
should  be  sent  to  the  chemical  laboratory. 

Oil  Testing  Machines. — The  coefficient  of  friction,  the  dura- 
bility, and  the  heat  removing  power  of  the  oil,  are  determined  by 
the  use  of  oil  testing  machines.  These  are  of  various  designs,  the 
form  used  in  several  U.  S.  Navy  laboratories  being  shown  in  Fig. 
123. 

The  main  journal  of  the  machine  rests  on  the  four  large  rollers, 
shown  in  the  figure.  This  reduces  friction  and  prevents  the  heating 
of  the  shaft,  which  would  affect  the  results  of  temperature  tests. 
Ball  thrust  collar  bearings  prevent  motion  along  the  direction  of 
the  axis  of  the  journal,  and  take  any  thrust  in  this  direction  that 
would  cause  friction. 

The  bearing  for  use  in  the  tests,  rests  on  the  top  of  the  journal, 
and  fits  in  a  cap,  to  which  the  yoke  frame  is  attached.  This  is  con- 
nected by  a  system  of  links  and  levers,  through  hardened  steel  sur- 
faces and  knife  edge  supports,  to  the  weighing  beam,  seen  on  the 
right.  A  turn  buckle,  concealed  under  the  frame  of  the  machine, 
enables  the  load  on  bearing  to  be  varied  by  the  operator  as  may  be 
desired.  The  amount  of  such  load  is  weighed  \)j  the  beam. 

The  diameter  of  journal  is  6  inches.     The  bearing  is  4  inches 


EXPERIMENTAL  ENGINEERING 

long  by  2%  inches  wide.  This  gives  a  projected  area  of  10  square 
inches,  but  after  determining  the  direction  in  which  the  machine  is 
to  run,  the  leading  edge  of  this  brass  is  shaped  down  in  a  horizontal 
plane  so  as  to  reduce  this  area  by  one  square  inch,  removing  the 
sharp  edge  to  permit  ready  access  of  oil  and  bringing  the  projected 
area  of  bearing  to  9  square  inches. 

In  the  center  at  top  of  cap  is  a  hole  for  thermometer  well.  This 
is  carried  into  the  cap  brass  to  within  J  inch  of  the  bearing  sur- 
face, and  a  J-inch  gas  pipe  nipple  is  screwed  in  to  seal  the  joint 
between  cap  and  brass.  A  standard  thermometer  is  provided  for 
use  in  the  well  in  making  tests.  The  space  in  well  around  ther- 
mometer is  filled  with  some  good  lubricating  oil  in  order  to  make 
contact  between  the  brass  and  the  bulb  of  thermometer. 

In  making  a  test,  after  the  machine  is  in  operation,  the  pres- 
sure is  applied  by  setting  out  the  poise  on  the  pressure  beam  to 
the  desired  point  and  then  tightening  the  turn  buckle  until  the 
beam  is  balanced.  Before  the  first  test  is  made,  the  total  weight  of 
the  parts  whose  weight  is  sustained  by  the  bearing  must  be  deter- 
mined, and  this  amount,  which  is  approximately  500  pounds,  must 
always  be  added  to  the  pressure  given  by  the  beam,  in  order  to  ob- 
tain the  total  pressure  on  the  bearing.  When  the  poise  is  at  1000 
pounds  the  total  pressure  on  the  bearing  will  be  1000  plus  500,  or 
1500  pounds,  approximately. 

Methods  of  Conducting  Tests. — No  standard  method  of  conduct- 
ing a  test  of  lubricating  oils  has  been  generally  adopted.  In  gen- 
eral the  object  of  a  test  is  to  determine  the  coefficient  of  friction. 
The  usual  method  is  to  run  the  machine  at  a  given  speed  and  under 
a  given  pressure  on  bearing.  Under  these  conditions,  if  the  load 
is  not  excessive,  and  a  sufficient  quantity  of  lubricant  is  supplied, 
the  temperature  will  rise  to  a  certain  point  and  remain  approxi- 
mately constant.  Four  methods  of  observation  are  then  practiced : 
First,  to  note  the  temperature  at  the  end  of  a  given  time;  second,  to 
note  the  time  necessary  to  reach  a  given  temperature ;  third,  to  note 
the  temperature  to  which  the  bearing  rises  and  at  which  it  remains 
constant  for  a  given  time;  fourth,  to  maintain  the  bearing  at  a 
given  temperature  by  cooling  it.  The  third  method  is  commonly 
used  because  it  is  easier  to  carry  out  and  more  nearly  approximates 
the  running  conditions  of  a  bearing. 


ENGINE  LUBRICATION  225 

To  conduct  a  test  according  to  the  third  method:  Clean  the 
journal,  bearing,  and  pad  with  gasoline  in  order  to  remove  all  traces 
of  lubricating  oil.  Soak  the  pad  with  the  sample  oil  and  also  apply 
it  freely  to  the  journal  and  bearing.  Eun  the  machine  a  few  min- 
utes, until  the  bearing  is  well  lubricated,  then  apply  the  desired 
pressure  by  means  of  the  turn  buckle  as  has  been  described.  The 
machine  must  be  run  at  a  constant  speed,  or  if  there  is  a  variation 
of  speed  it  must  be  slight,  and  readings  of  the  revolutions  per  minute 
must  be  taken  in  order  to  obtain  the  average.  Keep  a  log  of  the 
test,  taking  readings  of  the  revolutions,  temperature,  and  friction, 
every  five  minutes,  and  continue  until  the  temperature  remains  con- 
stant for  thirty  minutes.  Record  the  following  data :  Date,  kind  of 
lubricant,  total  pressure  on  bearing,  pressure  in  pounds  per  square 
inch  of  projected  area,  friction  load,  revolutions  per  minute,  velocity 
in  feet  per  minute,  duration  of  test,  temperature  of  room,  tempera- 
ture of  bearing  at  start,  temperature  of  bearing  when  constant.  Cal- 
culate the  coefficient  of  friction  and  make  it  a  part  of  this  record. 
To  calculate  the  coefficient  of  friction,  divide  the  friction  load,  as 
obtained  from  the  friction  beam,  by  the  total  pressure  in  pounds  on 
the  bearing. 

Navy  Department  Method. — The  following  method  of  testing 
oil  has  been  evolved  by  Mr.  C.  A.  Webb,  in  charge  of  the  testing 
laboratory,  Department  of  Steam  Engineering,  Navy  Yard,  New 
York,  where  a  machine  of  this  description  has  been  in  use  for  sev- 
eral years.  The  results  and  conditions  of  the  test  are  embodied  in 
specifications  for  lubricating  oil  for  marine  machinery,  issued  by 
the  Bureau  of  Supplies  and  Accounts,  Navy  Department.  The 
object  of  the  test  is  to  determine  the  wearing  quality  of  the  oil, 
although  the  coefficient  of  friction  is  also  obtained. 

The  accessories  with  the  machine,  necessary  for  this  test,  are,  a 
pair  of  laboratory  scales,  preferably  in  glass  door  case,  a  small  copper 
cup  of  4  ounces'  capacity  to  hold  the  oil,  and  an  orange  wood  stick 
about  J  inch  diameter  by  6  inches  long,  shaved  to  a  thin  blade  for 
half  its  length.  The  oil  pad  and  water-cooling  device  for  the  jour- 
nal are  not  used  in  this  test. 

The  directions  for  making  a  test,  as  given  by  Mr.  Webb  are  as 
follows : 

15 


226  EXPERIMENTAL  ENGINEERING 

(1)  Clean  the  bronze  bearing  and  journal  with  gasoline,  using  a 
cloth  to  wipe  them  dry. 

(2)  Weigh  about  half  an  ounce  of  the  oil  to  be  tested,  together 
with  the  oil  stick,  in  cup,  and  call  it  Weight  of  Oil  at  Start. 

(3)  Apply  a  small  amount  of  this  oil  to  the  bearing  and  journal; 
place  bearing  in  place  on  journal  and  apply  the  full  load. 

(4)  Place  the  thermometer  for  taking  temperature  of  bearing  in 
its  place,  and  after  reading  thermometers,  counter,  and  time,  start 
the  machine. 

(5)  At  the  instant  the  machine  is  started  a  drop  of  oil  from  the 
cup  should  be  applied  to  the  journal  on  the  advancing  side,  where 
the  bearing  touches  the  journal,  and  spreading  the  oil  so  as  to  make 
a  uniform  lubrication.    All  oil  used  on  test  will  be  applied  so,  pass- 
ing the  stick  backwards  and  forwards  along  the  face  of  the  bearing, 
spreading  the  oil  evenly.     If  the  pull  in  pounds  increases  in  spite 
of  the  spreading,  apply  fresh  oil  from  the  cup  until  the  pull  falls 
back  or  becomes  less.    The  pull  in  pounds  should  fall  to  normal  in 
about  20  minutes  from  start  to  test.    Keeping  the  poise  on  friction 
beam  just  balanced  while  the  oil  is  uniformly  spread,  the  proper 
amount  of  oil  can  be  easily  found  ;  for,  as  the  temperature  increases 
the  pull  decreases,  until  the  oil  has  reached  its  best  working  tem- 
perature.    As  long  as  the  pull  does  not  increase  with  a  uniform 
lubrication  by  spreading  with  the  stick,  it  does  not  require  fresh  oil, 
but  as  soon  as  the  pull  overbalances,  a  little  fresh  oil  will  bring  it 
back  to  balance.    Keep  poise  advancing  and  in  balance  while  spread- 
ing the  oil.    The  first  half  hour  will  in  most  cases  finish  the  applying 
of  fresh  oil,  and  the  last  hour  and  a  half  will  require  constant 
spreading.     The  temperature  and  pull  will  reach  the  normal  read- 
ing for  the  oil  under  test  in  the  first  hour,  and  remain  so  to  the  end, 
as  a  rule. 

(6)  At  the  end  of  the  two  hours,  read  the  counter  and  weigh  the 
oil  cup  with  stick  and  remaining  oil.    The  difference  in  weight  in 
grains  Troy  gives  the  weight  of  oil  used  for  the  test.    The  reading 
of  counter  will  give  the  revolutions  for  the  two  hours,  from  which 
we  get  the  average  revolutions  per  minue,  and  work  up  the  results. 

Circumference  of  journal  in  feet  x  R.  P.  M.  x  load  —  not  less 

Troy  grains  of  oil  than  325,000. 

pounds 


Coefficient  of  friction  = 


Total  load 


ENGINE  LUBRICATION 


227 


Before  starting  the  machine,  the  weight  beam  is  adjusted  to 
exactly  counterbalance  the  weight  of  framing  and  the  friction  beam 
arms  are  also  brought  to  equipoise.  A  load  of  2700  pounds  is  then 
added  to  the  brass  by  the  weight  beam  scales,  equalling  300  pounds 
per  square  inch  of  projected  area.  This  is  the  standard  load  for  all 
these  tests.  A  starting  load  of  about  100  pounds  is  also  put  on  that 
friction  beam  which  is  behind  the  direction  of  rotation  of  top  of 
journal.  This  is  subject  to  further  adjustment  during  the  tests. 

The  number  325,000  in  the  above  formula  is  the  coefficient  of 
performance,  which  must  be  reached  by  an  oil  in  order  for  it  to 
be  accepted.  It  does  not  indicate  the  foot  pounds  of  work  done  per 
grain  of  oil,  but  is  simply  an  arbitrary  standard.  The  coefficient  of 
friction  is  not  specified  in  the  requirements  for  oil,  but  it  indirectly 
governs  the  limit  of  temperature  and  the  quantity  of  oil  used. 

Log  of  Test. — 


Sample: 


OIL  FRICTION  TEST. 
Date: 


Time 

Temp. 

Load                               Speed 

Friction 

Air 

Bearing 

Total 

Sq.In. 

Counter 

Total  Ft. 

B.  P.  M. 

Pull  Lbs. 

Coef. 

Specification  = 


Circum.  journal  in  feet  x  R.  P.  M  x  load 


Troy  grains  oil 


>  325,000. 


Pull  in  pounds 

Coeftcient  fnct  on  =  

Total  load 


Tests  of  Oil  on  Board  Ship. — Attempts  to  improvise  a  testing 
machine  on  board  ship  will  be  found  unsatisfactory.  Tests  have 
been  made  utilizing  a  lathe  with  mandrel  to  improvise  a  testing 
machine.  The  bearing  surface  thus  used  must  necessarily  be  small 
and  it  will  be  found  difficult  to  apply  and  measure  a  sufficient  load 
for  the  test.  Such  apparatus  can  only  give  an  approximate  means 
of  comparison  with  another  oil  of  known  good  quality. 

A  sample  of  the  oil  under  examination  is  sometimes  used  to  lubri- 
cate the  bearings  of  some  part  of  the  auxiliary  machinery  that  is  in 


228  EXPERIMENTAL  ENGINEERING 

constant  use.  This  is  not  very  satisfactory  since  it  will  be  difficult 
to  completely  remove  all  particles  of  the  old  oil  before  beginning 
with  the  sample.  A  mixture  of  two  different  oils  will  frequently 
give  very  different  results  from  those  obtained  with  either  one  of 
them  when  used  alone.  An  instance  is  on  record  where  a  mixture 
of  two  of  the  best  known  engine  oils,  made  by  different  manu- 
facturers,, when  used  in  a  thrust  bearing,  caused  a  heavy  deposit  of 
paraffine,  with  consequent  heating  of  the  bearing.  Either  oil,  when 
used  alone,  was  perfectly  satisfactory. 

The  only  certain  test  of  a  lubricating  oil  is  to  use  it  for  the 
lubrication  of  a  bearing  under  service  conditions  and  the  test 
should  be  continued  long  enough  to  be  conclusive.  In  a  testing 
machine  the  bearing  is  set  up  close  and  the  load  applied  is  con- 
stant. In  service  there  is  clearance  in  the  bearing  and  the  load  is 
irregularly  applied,  in  extreme  cases  coming  in  the  form  of  heavy 
blows. 

Tests  in  an  oil  testing  machine  on  shore  are  of  value  in  indi- 
cating the  probable  character  of  a  new  brand  of  oil,  but  the  final 
test  must  be  that  of  actual  service.  In  beginning  the  use  of  a  new 
brand  care  must  be  taken  to  carefully  clean  out  all  the  old  oil. 

In  general  it  may  be  said  that  no  lubricating  oil  should  be  pur- 
chased for  use  on  board  ship  that  has  not  been  carefully  tested,  or 
the  character  of  which  is  not  guaranteed  by  a  well-known  brand, 
sold  by  a  reputable  dealer.  Such  brands  are  sold  all  over  the  world 
and  it  is  poor  economy  to  save  a  few  cents  on  the  gallon  in  the 
purchase  of  an  oil  that  is  of  inferior  quality.  When  using  an  in- 
ferior oil  there  is  danger  of  overheating  the  bearings,  causing  dam- 
age that  will,  besides  crippling  the  ship,  result  in  a  cost  for  repairs 
many  times  exceeding  the  amount  saved  in  the  purchase  of  the  oil. 


CHAPTEE  X. 
THE  SELECTION  AND  TESTING  OF  FUEL. 

Fuel  Economy. — Economy  in  fuel  consumption  is  influenced  in 
two  ways.  (1)  By  practicing  the  greatest  possible  economy  in 
burning  the  fuel.  (2)  By  selecting  fuel  that  is  best  adapted  to  the 
conditions  under  which  it  is  to  be  burned  and  that  will  develop  the 
greatest  amount  of  heat  from  a  given  quantity  of  the  fuel.  For 
commercial  uses  the  last  consideration  is  stated  in  another  way,  the 
desire  being  to  select  a  fuel  that  will  produce  the  greatest  quantity 
of  heat  at  the  lowest  cost.  This  consideration  also  holds  in  select- 
ing ji  fuel  for  naval  consumption,  but  it  is  not  of  paramount  im- 
portance, since  considerations  of  military  efficiency  often  lead  to  the 
selection  of  a  more  expensive  fuel  on  account  of  its  higher  heating 
value. 

Selecting  Coal. — The  following  qualities  in  coal  govern  its  selec- 
tion for  use  as  a  fuel : 

(1)  Percentage  of  Moisture. — The  moisture  present  in  coal  rep- 
resents a  dead  loss  on  account  of  its  weight.     Contracts  for  coal 
should  be  based  on  the  net  weight  of  dry  coal. 

(2)  Percentage  of  Volatile  Matter. — Boilers  must  have  a  large 
combustion  chamber  space  in  order  to  efficiently  burn  coal  con- 
taining a  high  percentage  of  volatile  matter.     Such  coal  must  also 
be  handled  differently  in  firing.     Where  the  coal  is  fired  by  hand 
there  should  be  no  great  variation  in  the  percentage  of  volatile 
matter,  since  it  will  in  that  case  be  necessary  to  train  the  firemen 
anew  with  each  variable  lot  of  coal  received. 

(3)  Percentage  of  Ash. — This  is  of  importance  as  it  affects  the 
heating  value  and  there  is  a  further  direct  loss  in  cleaning  fires. 
If  the  ash  is  fusible,  making  heavy  clinkers,  these  choke  the  grate 
and  prevent  efficient  combustion. 

(4)  The  Size  of  the  Coal. — Lump  coal  as  a  rule  burns  better 
than  fine  slack  coal,  though  if  slack  coal  cokes  readily  it  will  burn 


230  EXPERIMENTAL  ENGINEERING 

efficiently.  Some  of  the  best  American  steaming  coals  come  with  a 
very  small  proportion  of  lump.  Foreign  coals  should  as  a  rule  be 
avoided  when  there  is  not  a  large  proportion  of  lump. 

(5)  Heating  Value. — This  is  the  most  important  quality  of  all. 
It  is  stated  as  the  number  of  B.  T.  IPs  per  pound  of  dry  coal,  or 
combustible.  The  term  dry  coal  is  used  to  signify  that  from  which 
all  moisture  has  been  driven  off,  or  the  net  weight,  deducting  for 
the  percentage  of  moisture.  The  term  combustible  is  used  to  desig- 
nate the  net  weight,  deducting  for  the  percentage  of  ash. 

For  naval  use  the  coal  having  the  highest  heating  value  should 
as  a  rule  be  selected,  since  the  bad  qualities  usually  increase  in  in- 
verse proportion  to  the  heating  value,  and  military  necessity  impels 
us  to  fix  upon  a  high  grade  of  coal  and  require  all  contractors  to 
furnish  coal  of  this  grade.  This  may  also  be  the  most  economical 
policy  in  point  of  cost,  since  with  an  unknown  brand  of  coal  of 
mferior  quality,  the  firemen  who  are  unaccustomed  to  it,  are 
likely  unknowingly  to  waste  enough  to  more  than  make  up  for  the 
difference  in  cost. 

For  commercial  purposes  it  is  now  becoming  the  general  practice 
to  contract  for  coal  on  the  basis  of  its  heating  value  per  unit  of 
cost.  Where  a  low  price  can  be  thus  obtained  it  is  often  possible  in 
a  stationary  plant  to  make  what  arrangements  are  necessary  to  burn 
such  coal  for  a  long  period  of  time,  the  arrangements  and  the  con- 
tract being  made  with  a  view  to  producing  the  required  power  at  the 
lowest  price  during  the  time  for  which  the  contract  is  to  run. 

Testing  Coal. — Whatever  may  be  the  policy  with  regard  to  the 
quality  of  fuel  that  is  to  be  used,  it  becomes  of  necessity  to  test  the 
coal  that  is  under  consideration,  either  practically,  by  burning  it 
under  service  conditions,  or  by  careful  tests  in  a  properly  equipped 
laboratory.  For  a  test  on  shipboard,  the  only  practicable  procedure 
is  to  obtain  as  large  a  sample  as  possible  and  burn  it  on  the  grate 
of  a  boiler.  The  grate  should  be  clean  to  start  the  test  and  the 
sample  should  be  large  enough  to  make  a  thorough  test  under  full 
service  conditions. 

Sampling  Coal  for  Test. — The  object  in  taking  a  sample  of  coal 
is  to  obtain  a  small  portion  which  represents  as  nearly  as  possible 
the  entire  lot  of  coal  which  is  under  consideration. 


THE  SELECTION  AND  TESTING  OF  FUEL  231 

The  original  sample  should  preferably  be  collected  in  a  large 
receptacle  with  cover  attached,  by  taking  small  shovelsful  from 
many  parts  of  the  car,,  barge,  or  vessel  as  it  is  being  unloaded,  or 
from  as  nearly  all  parts  of  a  pile  as  possible,  care  being  taken  in 
all  cases  to  secure  practically  the  same  amounts  from  the  top, 
middle,  and  bottom  of  the  pile.  If  sampling  for  a  service  test,  the 
amount  taken  should  be  at  least  sufficient  for  a  day's  steaming 
under  service  conditions.  If  for  a  laboratory  test,  the  first  sample 
should  amount  to  500  pounds,  or  more,  preferably  1000  to  2000 
pounds.  A  separate  sample  should  be  taken  from  each  1000  tons 
or  less  delivered.  The  gross  sample  thus  collected  should  contain 
the  same  proportion  of  lump  and  fine  coal  as  exists  in  the  whole 
shipment.  It  should  be  protected  from  the  weather,  in  order  to 
avoid  gain  or  loss  in  moisture  and  should  be  immediately  quartered 
down  to  a  smaller  sample,  according  to  the  following  method : 

The  large  lumps  of  coal  and  impurities  should  be  broken  down 
on  a  clean,  hard,  dry  floor,  with  a  suitable  maul  or  sledge.  The 
coal  should  be  thoroughly  mixed  by  shovelling  it  over  and  over  and 
formed  in  a  conical  pile.  The  pile  should  then  be  quartered,  using 
a  shovel  or  board  to  separate  the  four  quarters.  Two  opposite 
quarters  should  then  be  rejected  and  the  remaining  two  broken 
down  to  a  smaller  size,  mixed  and  reformed  in  a  conical  pile  and 
quartered  as  before.  This  process  should  be  continued  until  the 
lumps  are  J  inch  in  size,  or  smaller,  and  a  one  or  two-quart  final 
sample  remains.  All  of  this  final  sample  should  immediately  be 
placed  in  one  or  more  glass  or  metal  cans  and  sealed  air-tight.  The 
outside  of  the  can  §  should  be  plainly  labelled  and  a  corresponding 
description  placed  inside  the  can. 

In  preparing  a  sample  the  work  should  be  carried  on  as  rapidly 
as  possible  in  order  to  avoid  loss  of  moisture  through  contact  with 
the  air. 

Test  for  Moisture. — A  portion  is  accurately  weighed  into  an 
oven  and  dried  for  one  hour  at  a  temperature  of  about  105°  F. 
Then  reweighing,  the  difference  gives  the  percentage  of  moisture. 

Test  for  Volatile  Matter.— A  portion  of  dry  coal  should  be 
weighed  into  a  flask  and  heated  to  incandescence  for  about  fifteen 
minutes.  This  will  drive  off  the  volatile  matter  and  on  reweigh- 


232  EXPERIMENTAL  ENGINEERING 

ing,  the  difference  gives  the  percentage  of  volatile  matter.  This 
test  is  sometimes  carried  out  on  an  open  tray,  but  this  requires  a 
very  careful  adjustment  of  temperature.  If  not  hot  enough  some 
of  the  volatile  matter  will  remain  and  if  too  hot  some  of  the 
carbon  will  be  consumed.  In  computing  the  percentage  of  volatile 
matter  the  calculation  must  be  based  on  the  weight  of  that  portion 
of  the  sample  of  coal  which  is  used,  that  is  before  either  the  moist- 
ure or  the  volatile  matter  is  driven  off. 

Test  for  Ash. — A  portion  of  the  sample  is  weighed  on  a  platinum 
dish,  then  heated  in  the  open  air  until  all  combustible  matter  is 
burned.  The  weight  of  the  residue,  compared  with  that  of  the 
portion  used  gives  the  percentage  of  ash.  The  value  thus  obtained 
is  the  actual  net  value  and  is  lower  than  it  is  possible  to  obtain 
when  burning  the  coal  on  a  grate,  owing  to  the  sifting  through  of 
fine  particles  of  combustible  with  the  ash.  The  loss  due  to  this 
cause  may,  with  careless  firing,  be  very  large  and  every  effort 
should  be  made  to  reduce  it  as  low  as  possible. 

Measurement  of  the  Heating  Value  of  Fuels. 

The  methods  of  calculating  the  theoretical  heating  value  of  a 
fuel,  its  evaporative  power,  the  amount  of  air  required  to  burn  it, 
the  temperature  of  the  furnace  that  it  is  possible  to  obtain  and  the 
method  of  conducting  boiler  tests  have  been  given  in  other  text- 
books. 

This  work  will  include  under  this  heading  only  such  apparatus 
as  is  used  in  the  experimental  determination  of  the  heating  power 
of  a  fuel. 

Mahler's  Calorimeter. — This  instrument  is  perhaps  the  best 
known  of  the  bomb  calorimeters,  in  which  a  sample  of  the  fuel  under 
test  is  burned  in  a  bomb  immersed  in  water  and  the  amount  of  the 
heat  of  combustion  is  measured  by  the  rise  in  temperature  of  the 
water. 

Principle  of  the  Apparatus. — The  combustible  is  placed  in  a 
closed  bomb,  made  strong  enough  to  resist  h^avy  pressure.  Oxygen 
is  introduced  under  pressure  and  the  gases  of  combustion  are  con- 
fined in  the  bomb.  The  bomb  is  immersed  in  the  water  of  the  cal- 
orimeter and  the  combustion  is  started  by  an  ignition  contrivance. 


THE  SELECTION  AND  TESTING  OF  FUEL  233 

On  account  of  the  large  quantity  of  oxygen  the  combustible  burns 
completely  and  almost  instantaneously.  Its  heat  is  given  off  and 
transmitted  to  the  water  and  to  the  various  parts  of  the  apparatus, 
such  losses  as  occur  being  easily  estimated  in  all  calorimetric  opera- 
tions. Owing  to  the  rapidity  of  the  operation  most  of  the  correc- 
tions that  would  be  made  in  a  physical  laboratory  become  negligible ; 
for  example,  that  which  takes  account  of  the  evaporation  of  the 
water. 

Description  of  the  Apparatus. — The  apparatus  is  shown  in  Fig. 
124,  in  which  A  is  the  water  jacket,  B  the  bomb  of  enamelled  steel, 
0  the  platinum  tray  for  holding  the  fuel,  D  the  calorimeter,  E  an 
electrode,  F  a  piece  of  fine  iron  wire  for  priming,  G  the  support 
for  agitator,  K  the  mechanism  of  agitator,  L  the  lever  for  operat- 
ing, M  a  pressure  gage  for  oxygen,  0  the  flask  of  oxygen,  P  an 
electric  battery,  8  the  agitator,  T  the  thermometer,  Z  a  clamp  for 
holding  the  bomb  while  removing  or  replacing  the  cap. 

The  bomb  is  of  forged  steel  of  the  best  quality.  It  is  of  about 
650  cc.  capacity,  with  walls  8  mm.  in  thickness.  This  capacity  is' 
such  as  to  assure  in  all  cases  perfect  combustion  of  the  fuel  by  a 
considerable  excess  of  oxygen.  It  also  enables  the  bomb  to  be  used 
for  experiments  on  gases  and  gas  mixtures  containing  as  much  as 
70%  of  inert  matter,  where  it  is  necessary  to  take  a  large  quantity 
if  a  rise  in  temperature  is  to  be  obtained  sufficiently  great  for  satis- 
factory results. 

The  bomb  is  nickel-plated  on  the  outside.  On  the  inside  a  coat  of 
enamel  preserves  it  against  the  action  of  nitric  acid,  which  is  al- 
ways formed  during  the  combustion.  The  bomb  is  closed  by  a  cap, 
screwed  down  on  a  lead  gasket.  This  cap  has  a  valve  in  its  center, 
with  screwed  nozzle  for  connecting  to  the  flask  of  oxygen.  It  is  also 
pierced  by  a  platinum  electrode,  well  insulated,  prolonged  on  the 
inside  by  a  platinum  rod  E.  A  second  platinum  rod,  fixed  to  the 
cap,  sustains  the  platinum  tray  C,  which  carries  the  sample  of  fuel 
under  test, 

A  spiral  of  very  fine  iron  wire  connects  C  with  E,  coming  in  con- 
tact with  the  fuel  when  the  bomb  is  charged.  When  the  current  is 
turned  on  this  wire  is  heated  to  redness,  then  burns  in  the  atmos- 
phere of  oxygen,  igniting  the  fuel. 


N 


THE  SELECTION  AND  TESTING  OF  FUEL  235 

The  agitator  consists  of  vanes,  carried  on  a  central  rod  with  spiral 
thread  passing  through  a  fixed  nut.  It  is  operated  by  a  lever  which 
permits  the  operator  to  systematically  stir  the  water  in  the  calo- 
rimeter, thus  ensuring  an  even  temperature. 

The  valve  on  flask  does  not  have  a  fine  enough  adjustment  to 
permit  gradual  introduction  of  the  oxygen.  A  second  valve,  not 
shown  in  the  figure,  having  a  very  fine  adjustment,  is  placed  in  the 
connection  to  tank  for  this  purpose.  The  figure  shows  a  flask  for 
oxygen  containing  about  1000  liters.  It  is  ordinarily  supplied  in 
this  manner  at  about  120  atmospheres  pressure.  Since  the  pres- 
sure convenient  for  the  combustion  of  one  gram  of  coal  is  only 
about  25  atmospheres,  there  is  thus  a  provision  for  about  60  tests. 

A  high-grade  thermometer  reading  to  1/50°  C.,  an  electric  bat- 
tery of  12  volts  and  2  amperes  capacity,  and  a  stop-watch  complete 
the  apparatus. 

Determination  of  the  Calorific  Value. — The  following  method 
of  procedure  for  determining  the  calorific  value  of  a  solid  or  liquid 
combustible  is  that  given  by  the  inventor  of  the  apparatus. 

One  gram  of  the  fuel  is  weighed  and  placed  in  the  tray  C.  The 
small  iron  wire  F  of  a  known  weight  is  adjusted  in  contact  with 
the  fuel  and  serves  as  a  primer.  After  having  introduced  all  in  the 
bomb,  it  is  placed  in  the  clamp  Z  and  the  cap  is  screwed  on  hard 
by  means  of  a  heavy  hexagonal  wrench. 

The  valve  on  cap  is  then  opened,  the  second  valve  for  fine  ad- 
justment having  first  been  closed.  The  valve  on  flask  is  opened 
and  then,  very  slowly,  the  adjusting  valve,  until  the  gage  indicates 
25  atmospheres.  After  having  closed  all  valves  the  tube  is  then 
disconnected. 

The  bomb,  thus  prepared,  is  placed  in  the  calorimeter  D.  The 
thermometer  T  and  agitator  8  are  placed  in  position  and  a  meas- 
ured quantity  of  water,  sufficient  to  completely  cover  the  bomb,  is 
poured  in.  This  quantity  will  be  about  2200  cc.,  which  is  the 
amount  used  by  M.  Mahler  in  his  experiments.  The  water  is 
stirred  for  some  minutes,  in  order  to  let  the  whole  system  arrive  at 
an  even  temperature,  then  observations  are  commenced. 

The  temperature  is  noted  from  minute  to  minute  for  5  minutes, 
in  order  to  fix  the  rate  of  variation  of  the  thermometer  before  igni- 


236  EXPERIMENTAL  ENGINEERING 

tion.  At  the  end  of  the  fifth  minute  contact  is  made  and  the  fuel 
fired  by  means  of  the  battery  connected  to  the  electrode  E  and  to  a 
point  on  the  valve.  Ignition  takes  place  immediately. 

The  temperature  is  noted  half  a  minute  after  the  contact  is  made, 
then  at  the  end  of  a  minute,  and  the  observations  are  continued  from 
minute  to  minute  up  to  the  point  where  the  thermometer  commences 
to  fall  regularly.  This  is  the  maximum. 

The  observations  are  then  continued  for  five  more  minutes  in 
order  to  fix  the  rate  of  variation  of  the  thermometer  after  it  reaches 
the  maximum. 

The  principal  data  for  the  calculations  are  then  at  hand,  in- 
cluding data  for  the  correction  for  loss  of  heat  by  radiation  from 
the  calorimeter.  This  correction  is  made  according  to  the  following 
rules,  true  between  large  limits,  even  where  the  amount  of  con- 
tained water  is  not  more  than  half  the  water  equivalent  of  the 
calorimeter. 

(1)  The  rate  of  decrease  of  temperature,  observed  after  reaching 
the  maximum,  represents  the  rate  of  loss  of  heat  from  the  calorim- 
eter before  reaching  the  maximum,  provided  the  fall  in  temperature 
is  not  greater  than  1°  C.  per  minute. 

(2)  If  the  fall  in  temperature  per  minute  is  greater  than  1°,  but 
less  than  2°  C.,  the  figure  representing  the  rate  of  decrease,  when 
diminished  by  0.005,  gives  the  desired  correction. 

The  two  preceding  paragraphs  cover  all  cases.  It  is  possible  also, 
and  that  without  altering  the  accuracy  of  the  experiment,  to  con- 
sider the  variation  during  the  first  half  of  the  minute  following  the 
ignition  as  that  which  exists  at  the  minimum  temperature. 

During  the  whole  experiment,  the  observer  should  continually 
operate  the  agitator. 

When  the  observations  are  ended,  the  valve  on  the  bomb  is  first 
opened,  then  the  bomb  itself.  The  bomb  will  contain  the  ordi- 
nary products  of  combustion,  composed  principally  of  carbonic  acid 
gas  and  water,  a  considerable  quantity  of  free  oxygen,  and  an  appre- 
ciable quantity  of  nitric  acid  formed  during  the  combustion  from 
such  nitrogen  as  was  present  in  the  bomb  at  atmospheric  pressure 
before  it  was  charged  with  oxygen. 

The  interior  of  the  bomb  is  washed  with  a  small  quantity  of  water 


THE  SELECTION  AND  TESTING  OF  FUEL  237 

to  remove  the  liquid  acid  formed  during  the  explosion.  The  amount 
of  nitric  acid  is  then  determined  by  a  simple  chemical  analysis,  and 
the  calorific  value,  h,  is  determined  from  the  formula : 

fc  =  r(l  +  a)(P  +  P')-(230p  +  1600p'),  wnere 
r  =:  the  rise  in  temperature. 

a  =  the  loss  of  temperature  during  the  experiment. 
P  =  the  weight  of  water  in  the  calorimeter. 
P'  =  the  water  equivalent  of  the  calorimeter. 
p  —  the  weight  of  nitric  acid. 
p'  =  the  weight  of  the  iron  ignition  wire. 
230  =  the  heat  of  formation  of  one  gram  of  nitric  acid. 
1600  =  the  heat  of  combustion  of  one  gram  of  iron. 

In  making  a  test  of  coal  no  separate  account  is  taken  of  the 
quantity  of  sulphuric  acid,  resulting  from  the  oxidation  of  the  small 
quantity  of  sulphur  present  in  the  sample,  such  acid  being  treated 
as  nitric  acid.  The  error  is  negligible  in  ordinary  work.  It  may  be 
noted  that  the  sulphur  being  entirely  oxidized  and  transformed  into 
sulphuric  acid,  the  bomb  gives  a  means  of  evaluating  it.  For  this 
purpose,  in  order  to  give  a  sufficient  quantity  for  satisfactory  opera- 
tion, it  will  be  better  to  burn  2  grams  under  30  atmospheres,  with- 
out taking  readings  of  the  thermometer. 

If  desired,  account  may  be  taken  of  the  heat  generated  by  the 
formation  of  sulphuric  acid,  which  is  0.73  calories  per  gram  of  acid. 

In  testing  a  substance  containing  but  little  hydrogen,  coke  for 
example,  so  little  water  of  combustion  is  formed  that  the  quan- 
tity is  insufficient  to  dissolve  the  acid.  It  is  then  best  to  place  in 
the  bottom  of  the  bomb  a  few  cc.  of  water,  which  must  be  taken 
into  account  in  making  the  calculations. 

The  procedure  is  the  same  for  a  liquid  as  for  a  solid.  If  the 
liquid  gives  off  vapors  it  is  well  to  weigh  the  sample  in  a  closed  vial, 
having  thin  points  through  which  is  passed  the  film  of  iron  wire. 
At  the  moment  of  introducing  the  vial  into  the  bomb,  care  should 
be  taken  to  break  these  points  in  order  to  bring  the  oxygen  into  con- 
tact with  the  liquid. 

M.  Mahler  has  also  used  the  apparatus  for  the  determination 
of  the  calorific  value  of  various  gases.  After  having  exhausted  the 
bomb  and  measured  the  pressure  remaining,  the  gas  is  introduced 


238  EXPERIMENTAL  ENGINEERING 

for  the  first  time.  The  bomb  is  then  exhausted  a  second  time,  after 
which  it  is  filled  with  the  gas  at  barometric  pressure  and  at  the  tem- 
perature of  the  laboratory.  The  oxygen  is  then  added  and  the  pro- 
cedure is  carried  on  in  the  same  manner  as  for  solid  and  liquid  fuels. 

The  determination  of  the  calorific  value  of  gases  offers  a  special 
difficulty.  If  diluted  with  too  great  a  quantity  of  oxygen,  the  mix- 
ture will  not  be  combustible.  For  illuminating  gas,  5  atmospheres 
will  be  sufficient.  For  producer  gas,  half  an  atmosphere  only  should 
be  used,  measured. on  a  mercurial  manometer. 

Determination  of  the  Water  Equivalent  of  the  System. — In 
order  to  determine  the  value  of  Pf,  the  term  representing  in  water 
the  exact  equivalent  of  the  system,  the  simplest  method  is  to  per- 
form a  double  experiment  as  follows: 

Burn  in  the  bomb  a  known  weight,  one  gram  for  example,  of  a 
combustible  or  fixed  composition,  such  as  fuel  oil,  and  with  2300 
grams  of  water  in  the  calorimeter.  Then  burn  the  same  weight  of 
the  same  combustible  with  only  2100  grams  of  water  in  the 
calorimeter. 

There  will  then  be  two  equations  between  which  the  heat  of  com- 
bustion of  the  fuel  may  be  eliminated  and  the  value  of  the  water 
equivalent  may  be  deduced. 

Example. — The  following  example  of  the  work  of  the  apparatus 
is  given  by  M.  Mahler : 

The  fuel  under  test  is  a  sample  of  colza  oil.  An  approximate 
analysis  gave : 

Carbon   77.182 

Hydrogen    11.711 

Oxygen  and  Nitrogen 11.107 


100.000 

Weight  of  sample  tested,  1  gram. 

Water  in  calorimeter,  2200  grams. 

Water  equivalent  of  the  bomb  and  accessories,  previously  deter- 
mined, 481  grams. 

The  apparatus  being  prepared  as  above  directed,  a  little  time  is 
allowed  to  elapse  for  the  temperature  to  equalize,  then  the  stop 
watch  is  started  and  the  temperatures  are  noted  as  below. 


THE  SELECTION  AND  TESTING  or  FUEL  239 

Preliminary  Period. 

0  minutes    ...................................  10°.23 

1  "          ...................................  10°.23 

2  "  ...................................  10°.24 

3  "  .........................    .........  10°.24 

4  "  ...................................  10°.25 

5  "  ...................................  10°.25 


5 

The  combustible  is  then  fired. 

Period  of  Combustion, 

5y2  minutes   .................................  10°.80 

6  minutes    ...................................  12°.90 

7  "          ...................................  13°.79 

8  "          ...................................  13°.84  (max.). 

Final  Period. 

9  minutes    ..................................  13°.82 

10  "    ..................................  13°.81 

11  "    ..................................  13°.80 

12  "    ..................................  13°.79 

13  "    ..................................  13°.78 


5 

No  further  readings  of  the  thermometer  are  taken. 
The  change  in  temperature  has  been  13°.84-10°.25  =  3°.59. 
Corrections.  —  The  apparatus  has  lost  during  the  minutes  (7,  8) 
(6,  7)  a  quantity  of  heat  measured  by 

13°.84-13°.78  X2  =  0°.012(1)X2  =  0°.024. 

During  the  half  minute  (5J,  6)   it  has  lost  a  quantity  of  heat 
represented  by 

(0°.012-0°.005)  xi  =  0°.0035. 

And  during  the  half  minute  (5,  5J)  it  gained 
10°.25-10°.23 


240  EXPERIMENTAL  ENGINEERING 

Finally,  the  loss  during  the  minute  (5,  6)  is 

0°.0035-0°.002  =  0°.0015. 
To  sum  up,  the  loss  during  the  whole  experiment  has  been 

0°.024  +  0°.0015  =  0°.0255, 

a  quantity  which  should  be  added  to  the  3°.  59  already  found. 

The  corrected  rise  in  temperature  is  then  3°.  6  15,  neglecting  the 
ten  thousandths. 

The  quantity  of  heat  observed  is  therefore 

(2200  +  481)  X3°.615  =  9691.8  calories. 

In  order  to  obtain  the  final  result  we  subtract  from  this  figure 

(1)  The  heat  of  formation  of  0.13  gram  of  nitric  acid,  deter- 
mined volumetrically,  0.13x230  =  29.9  cal. 

(2)  The   heat    of    combustion    of    0.025    gram    of    iron    wire, 
0.025x1600  =  40.0  cal. 

Amount  to  be  deducted,  69.9  cal. 

The  final  result  is  then  9691.8-69.9  =  9621.9  calories. 
Or,  for  a  kilogram  of  oil,  9621.9  kilo-calories. 
To  transform  this  result  into  B.  T.  U.  per  pound  of  oil,  multiply 
by  1.8. 

9621.9x1.8  =  17,319.42  B.  T.  U. 

Applying  the  formula  h  =  14,500  (C  +  4.28(71-0/8)  )  we  obtain 
for  h  the  theoretical  value  17,597. 

The  dimensions  of  this  apparatus  are  such  that  it  is  possible  to 
so  regulate  the  conditions  of  a  test  as  to  cancel  the  minor  correc- 
tions. If  a  is  the  correction  due  to  the  loss  of  heat  during  the 
operation,  it  will  be  seen  from  inspection  of  the  equation  on  page 
237,  that  it  will  not  be  necessary  to  take  into  account  such  correc- 
tions if 


since  the  equation  then  becomes  h  =  r(P  +  P'). 

Since  the  value  of  p  depends  chiefly  on  the  quantity  of  nitrogen 
contained  in  the  bomb  before  charging  with  oxygen,  it  will,  when 
testing  solid  or  liquid  fuel,  be  practically  constant,  p'  is  variable 
at  the  pleasure  of  the  operator  within  small  limits,  but  mav  also  be 


THE  SELECTION  AND  TESTING  OF  FUEL 


241 


given  a  constant  value.  It  is  possible  then  to  so  regulate  the  values 
of  a  and  P  that  the  above  equation  will  be  sufficiently  true  in  all 
ordinary  operations.  This  has  been  done  by  M.  Mahler  with  the 
apparatus  under  his  own  direction.  For  example,  the  calorific  value 
of  colza  oil  under  examination  was  found  to  be  9621.9  calories. 
Using  the  values  3.59  and  481  which  were  found  for  r  and  P' 
respectively,  we  have 

r(P  +  P')  =:3.59(2200  +  481)  =9624, 
which  approximates  very  closely  to  the  exact  result  obtained. 


FIG.  125. 

This  approximate  method  is  that  usually  followed  in  testing 
a  solid  or  liquid  fuel.  If  somewhat  greater  accuracy  is  desired,  the 
value,  p  =  Q.l3,  found  in  the  above  experiment  may  be  used  with  the 
observed  values  of  a,  p'  and  P.  In  testing  a  gas,  where  the  propor- 
tion of  nitrogen  is  large,  it  will  be  necessary  to  evaluate  the  quan- 
tity of  nitric  acid. 

Carpenter's  Improved  Coal  Calorimeter. — In  construction  this 
instrument  may  be  compared  to  a  thermometer,  in  the  bulb  of 
which  combustion  takes  place,  the  heat  of  combustion  being  ab- 
sorbed by  the  liquid  contained  in  the  bulb,  and  the  amount  of  this 
heat  being  proportional  to  the  expansion  of  the  liquid.  The  ex- 
pansion is  measured  by  the  rise  of  the  water  level  in  an  open  glass 
16 


242  EXPERIMENTAL  ENGINEERING 

tube,  from  which  the  number  of  B.  T.  IPs  absorbed  by  the  liquid 
is  determined.  As  set  up  for  use,  the  complete  apparatus  is  shown 
in  Fig.  125  and  consists  of  the  calorimeter  proper,  a  flask  of  oxygen, 
a  pressure  reducer  for  oxygen,  and  the  electric  firing  connections. 
Description. — Eeferring  to  Fig.  126 :  The  combustion  chamber, 
a,  is  supplied  with  oxygen  through  tube  b,  the  products  of  com- 
bustion being  conducted  through  spiral  tube  c,  c.  The  tube  ends 
in  a  hose  nipple  d,  from  which  a  hose  connection  is  made  to  a 
small  chamber  e,  attached  to  the  outer  case,  and  fitted  with  a 
manometer  /  for  measuring  the  pressure  of  combustion.  A  plug 
g,  with  pin  hole,  is  attached  to  the  chamber  for  the  discharge  of 
gases.  Surrounding  the  combustion  chamber  af  is  a  large  closed 
chamber  h,  filled  with  water  and  connected  to  the  open  glass  tube  i. 
The  level  of  water  in  i  is  measured  on  the  scale  /.  Above  the  water 
chamber  is  a  diaphragm  k  which,  by  means  of  the  screw  I,  is  used 
to  adjust  the  zero  level  to  any  desired  point  in  the  open  glass  tube  i. 
Glass  is  fitted  at  m,  n,  and  o,  so  that  the  process  of  combustion  may 
be  observed.  A  screw  plug  p,  is  removed  when  filling  or  emptying 
the  water  chamber.  The  plug  q,  which  stops  up  the  bottom  of  the 
combustion  chamber,  carries  a  dish  r,  in  which  the  fuel  for  com- 
bustion is  placed,  and  two  vertical  adjustable  insulated  wires  s,  s, 
the  upper  ends  of  which  are  joined  by  a  thin  platinum  wire. 
These  wires  are  connected  to  an  electric  battery,  or  circuit,  the 
current  of  which  is  used  for  firing  the  fuel.  A  silver  mirror  on 
top  of  the  plug  deflects  any  radiating  heat.  The  plug  itself  is  so 
constructed  and  fitted  that  little  or  no  heat  is  transferred  to  the 
outside,  but  practically  all  heat  is  rapidly  transmitted  to  the  sur- 
rounding water.  The  instrument  is  supported  on  strips  of  felting 
u  and  vf  and  fits  into  a  nickel-plated  case,  the  inside  of  which  is 
polished  to  reduce  radiation.  Eight  inches  water  pressure  has  been 
found  sufficient  for  combustion. 

The  sample  of  coal  to  be  tested  weighs  about  1J  grams  and  is 
burned  in  the  combustion  chamber  in  an  atmosphere  of  oxygen, 
kept  at  a  constant  pressure  of  8  inches  of  water.  Oxygen  is  re- 
ceived in  the  laboratory  in  heavy  flasks  under  about  sixty  atmos- 
pheres' pressure.  This  pressure,  in  the  ordinary  form  of  the  ap- 
paratus, is  reduced  by  throttling  to  the  low  pressure  used  for  com- 


THE  SELECTION  AND  TESTING  OF  FUEL 


243 


<P 


FIG.  126. 


244 


EXPERIMENTAL  ENGINEERING 


bustion.  The  reduction  is  so  great,  however,  as  to  make  perfect 
regulation  with  a  simple  throttle  valve  very  difficult.  It  has  been 
found  of  great  advantage  to  introduce  a  pressure  reducer  between 
the  flask  and  the  combustion  chamber.  This  apparatus,  as-  designed 
by  Lieutenant-Commander  F.  D.  Karns,  U.  S.  N.,  and  built  at 

o 


the  Naval  Academy,  is  shown  in  Fig.  127,  and  is  described  as  fol- 
lows: 

Pressure  Reducer  for  Oxygen. — Eeferring  to  Fig.  127:  A  is 
a  cylindrical  chamber  open  at  the  top  and  closed  at  the  bottom 
by  a  cap  R.  B  is  a  3-inch  pipe  lowered  into  A,  with  its  lower  end 
resting  on  three  studs  P,  as  shown.  The  upper  end  of  B  is  closed 


THE  SELECTION  AND  TESTING  OF  FUEL  245 

by  the  cap  C.  Studs  Q  serve  to  keep  B  upright.  Two  J-inch  pipes, 
D  and  E,  enter  the  lower  end  of  A,  pass  up  through  the  inside  of  B} 
with  their  open  ends  terminating  with  J  inch  of  cap  C.  Water 
fills  the  chamber  A  about  two-thirds  full  and,  with  valve  0  open, 
rises  to  the  same  level  m,  ra',  m,  in  A  and  B,  the  level  being  at  all 
points  under  atmospheric  pressure.  Oxygen  from  the  flask  under 
pressure  is  admitted  through  D  to  the  clearance  space  above  the 
water  level  in  B,  creating  a  pressure  with  valve  0  closed  that  forces 
some  of  the  water  out  of  B,  to  the  level  n',  thereby  causing  the 
level  in  A  to  rise  to  the  level  n,  n,  where  a  balance  is  established 
against  the  pressure  of  oxygen  in  B.  The  rise  of  the  water  is 
noted  in  the  gage  glass,  and  the  corresponding  pressure  in  inches 
of  water  is  read  off  on  the  attached  scale  F.  The  pressure  in  B  is 
controlled  by  means  of  the  throttling  valve  H  and  maintained  at 
12  inches  water  pressure,  which  is  found  to  be  that  best  suited  to 
the  test  requirements.  From  B  the  oxygen  is  conveyed  through 
the  pipe  E  and  valve  L,  where  it  is  further  throttled  and  kept  at  a 
pressure  of  8  inches  of  water  as  it  discharges  to  the  combustion 
chamber  of  the  calorimeter.  Valve  0  is  for  the  purpose  of  placing 
B  under  atmospheric  pressure  for  marking  off  the  zero  water  level. 
It  also  serves  to  permit  the  air  in  B  to  escape,  so  that  the  clearance 
space  may  be  completely  filled  with  pure  oxygen  before  beginning 
a  test. 

The  scale  F  is  graduated  to  read  in  inches  water  pressure,  the 
value  corresponding  to  any  observed  water  level  in  the  gage  glass 
being  determined  as  follows: 

Referring  to  Fig.  127  : 

Let  A^  =  area  of  cross  section  in  A  (annular  space). 
"     A 2  =  area  of  cross  section  in  B  (excluding  small  pipes). 
"     h^  —  amount  water  level  rises  in  A. 
"     h2  =  amount  water  level  falls  in  B. 

7         ..    .      A 

Then  h2X A2  =  h^x A19  and  Ji2  = 
Head,  in  inches,  =hi-\-h2- 


A, 


A2 


since  A±  and  A2  are  both  known  constants.     h±  is  measured  by  the 
rise  of  the  water  in  the  gage  glass.     For  purposes  of  graduating 


246  EXPERIMENTAL  ENGINEERING 

the  scale,  the  "head"  is  marked  off  and  indicated  for  heights  hlf 
increasing  by  one  quarter  of  an  inch.  Assume  the  simplest  case, 
in  which  A1  =  A2.  Then  head  =  2hl:>  and  if  the  actual  rise  of  the 
water  is  one  inch,  the  corresponding  water  pressure  is  two  inches, 
and  would  be  so  marked  on  the  scale. 

Method  of  Conducting  a  Test. — (1)  Preparation  of  the  Sample. 
— Select  an  accurate  sample  by  a  system  of  quartering,  reduce  it 
to  powder,  place  in  a  dry  asbestos  cup  of  known  weight  and  weigh 
accurately. 

(2)  Adjustment  of  Gas  Pressure. — Open  valve   0  and  adjust 
zero  point  of  scale  F  to  water  level  in  gage  glass.    Exhaust  air  from 
clearance  space  of  B,  taking  care  that  no  water  enters  the  small 
pipes,  and  then  close  0.     Admit  oxygen  from  flask  through  pipe 
D  and  valve  H  until  water  level  rises  to  12  on  scale  F,  and  keep  it 
there  by  closing  or  manipulating  H.     During  this  time  valve  L  is 
kept  closed. 

(3)  Firing  the  Charge. — Introduce  coal  sample  into  calorimeter, 
raise  platinum  wire  above  coal,  make  battery  connection,  and  as 
soon  as  heat  from  wire  causes  water  in  glass  tube  to  begin  to  rise, 
turn  on  oxygen  gas  (by  opening  valve  L  at  the  reducer),  and  fire 
charge  by  pulling  heated  wire  down.    The  instant  coal  is  lighted, 
break  electric  connection  and  note  first  scale  reading  and  time. 
The  gas  pressure  in  the  combustion  chamber  must  be  kept  constant 
at  eight  inches  during  the  test,  and  this  is  done  by  properly  throt- 
tling the  valve  L,  noting  the  pressure  indicated  by  the  manometer 
attached  to  the  discharge  side  of  the  calorimeter. 

(4)  Actual  Scale  Reading. — Watch  the  combustion,  which  usu- 
ally requires  about  10  minutes  for  each  gram  of  coal,  and  when 
completed  note  second  scale  reading  and  time.     The  difference  be- 
tween second  and  first  scale  readings  is  the  "  actual "  scale  reading. 

(5)  Correction  for  Radiation. — Allow  the  calorimeter  to  stand 
for  a  time  equal  to,  and  under  the  same  conditions  as,  that  of 
combustion,  except  that  the  oxygen  gas  is  shut  off,  and  note  third 
scale  reading  and  time. 

(6)  Corrected  Scale  Reading. — The  difference  between  second 
and  third  scale  readings  is  the  correction  for  radiation,  and  must 
be  added  to  the  "  actual "  scale  reading  to  get  the  "  corrected " 
reading. 


THE  SELECTION  AND  TESTING  OF  FUEL  247 

(7)  To  Find  Calorific  Value. — From  the  calibration  curve  find 
the  heat  value  of  the  sample  in  B.  T.  U.  corresponding  to  the  "  cor- 
rected "  scale  reading,  and  divide  the  B.  T.  U.  thus  obtained  by  the 
weight  of  the  sample  in  pounds.     The  result  will  be  the  calorific 
value  in  B.  T.  U.  per  pound  of  coal. 

(8)  To  Determine  the  Ash. — Weigh  the  cup  in  which  combus- 
tion took  place,  with  its  contents.     From  this  weight  subtract  the 
known  weight  of  the  cup,  and  the  difference  will  be  the  weight  of 
the  ash  in  the  sample. 

General  Instructions. — (1)  To  prepare  for  another  test,  remove 
calorimeter  from  outside  case  and  immerse  in  cold  water  for  a  few 
minutes,  care  being  taken  to  prevent  any  water  entering  tubes  or 
combustion  chamber. 

(2)  It  is  important  that  the  water  in  the  calorimeter  should  be 
free  from  air  and  that  the  oxygen  gas  be  supplied  at  a  constant 
pressure. 

(3)  In  burning  coals  having  a  large  percentage  of  volatile  mat- 
ter, the  water  resulting  from  the  combustion  may  affect  the  rate  of 
flow  of  the  burned  gases,  and  thus  change  the  reading  of  the  ma- 
nometer.   In  this  case  the  result  of  the  test  is  of  uncertain  value. 

(4)  The  temperature  of  the  calorimeter  at  the  beginning  of  a 
test  should  be  a  few  degrees  above  that  of  the  surrounding  atmos- 
phere. 

(5)  Complete  combustion  will  always  be  obtained  when  asbestos 
cups  are  used. 

(6)  An  asbestos  cup   is  made  by  wrapping  a  piece  of   sheet 
asbestos  about  the  end  of  a  small  cylinder,  and  using  a  weak  glue 
to  hold  it  in  cup  form.     The  cup  is  then  heated  to  a  white  heat 
in  order  to  remove  any  combustible  matter.    The  cup  when  weighed 
must  be  dry. 

(7)  Oxygen  for  combustion  is  usually  purchased  in  condensed 
form  in  heavy  steel  flasks,  but  in  case  the  supply  should  at  any 
time  become  exhausted,  it  may  be  made  by  heating  a  mixture  of 
about  equal  parts  of  dioxide  of  manganese  and  chlorate  of  potash 
placed  in  a  closed  retort. 

(8)  Electric   current   for   heating   the   platinum   wire   may   be 
taken  from  a  dry  battery  or  reduced  from  a  lighting  circuit. 


248  EXPERIMENTAL  ENGINEERING 

(9)  The  calorimeter  will  give  good  results  only  when  all  the 
conditions  under  which  the  calibration  was  made  are  maintained 
during  the  test. 

Calibrating  the  Calorimeter. —  (1)  Preparation  of  Sample. — 
Reduce  some  charcoal  from  sugar  or  soft  coal  to  powder,  fill  a 
porcelain  or  clay  crucible  one-third  full,  cover  it  tightly,  and  heat 
it  by  means  of  a  blast  lamp  or  a  forge  fire  for  half  an  hour.  When 
cold,  grind  it  in  a  mortar  to  very  fine  powder.  Repeat  this  opera- 
tion for  other  samples  to  be  tested. 

(2)  To  Free  the  Water  in  the  Calorimeter  from  Air. — Connect 
the  glass  tube  opening  by  rubber  hose  with  a  smaller  vessel  filled 
with  water.    Boil  the  water  in  the  calorimeter,  using  a  burner  and 
protecting  the  calorimeter  by  a  thin  sheet  of  asbestos  paper.     All 
air  and  steam  will  pass  to  the  smaller  vessel,  which  must  be  kept 
boiling  until  the  calorimeter  has  cooled  off.     Then  remove  rubber 
connection  and  insert  glass  tube,  taking  care  that  no  air  is  trapped. 
The  instrument  is  now  ready  for  calibration. 

(3)  Testing  the  Sample. — Follow  the  instructions  already  given 
under  "  Method  of  Conducting  the  Test."    The  difference  between 
the  weight  of  cup  and  sample,  and  the  weight  of  cup  and  ash,  is 
the  weight  of  pure  carbon  burned.     Multiply  the  weight  of  pure 
carbon  burned  by  14,600  and  obtain  the  number  of  heat  units  in 
the  sample.    Find  this  for  several  weights. 

(4)  To  Construct  the   Curve  of  Calibration. — With  the  "cor- 
rected" scale  readings  as  ordinates,  and  the  corresponding  heat 
values  of  the  several  samples  burned  as  abscissa,  make  points  in 
crossing  and  through  these  points  draw  a  fair  curve.    All  the  points 
should  lie  on  a  straight  line  whose  origin  is  at  zero. 

The  calibration  curve,  shown  in  Fig.  128,  was  determined  as  the 
result  of  a  series  of  tests  made  in  the  Engineering  Laboratory. 

The  Parr  Standard  Calorimeter. — This  instrument,  devised  by 
Professor  S.  W.  Parr,  of  the  University  of  Illinois,  is  a  bomb 
calorimeter  in  which  the  fuel  under  test  is  placed  in  the  bomb  to- 
gether with  chemicals  containing  the  constituents  necessary  for  its 
complete  combustion  and  for  the  further  absorption  by  chemical 
combination  of  the  gases  given  off  in  the  process  of  combustion. 


THE  SELECTION  AND  TESTING  OF  FUEL 


249 


Slg 


NO  CM 


250 


EXPERIMENTAL  ENGINEERING 


The  instrument  is  shown  in  Fig.  129.  A  is  a  can  in  which,  for 
the  test,  two  liters  of  water  are  placed.  B  and  C  are  the  outer  and 
inner  walls  of  the  containing  vessel,  divided  by  an  air  space  be- 
tween them.  To  further  prevent  loss  of  heat  by  radiation,  they  are 
made  of  non-conducting  material. 


FIG.  129. 

Combustion  takes  place  in  the  bomb  D.  This  rests  on  a  pivot  and 
is  rotated  at  a  speed  of  about  100  revolutions  per  minute  by  means 
of  a  small  motor.  This  is  for  the  purpose  of  ensuring  a  uniform 
temperature  of  the  water,  which  is  thus  stirred  by  means  of  the 
vanes  shown  in  the  figure. 

Two  forms  of  ignition  are  used.     As  first  designed,  the  charge 


THE  SELECTION  AND  TESTING  OF  FUEL 


251 


-K 


B 


was  ignited  by  dropping  into  the  bomb  a  small  piece  of  red-hot 
wire.  The  bomb  as  fitted  later  for  electrical  ignition  is  shown  in 
section  in  Fig.  130.  A  is  the  shell  of  the  bomb.  B  is  the  tube 
whose  lower  end  fits  gas  and  water  tight  over  A. 
F  is  a  cap  for  securing  B.  C  is  the  bottom  of 
the  bomb,  secured  gas  and  water  tight  by  the  plug 
D.  G  is  the  ignition  wire,  which  passes  through 
tube  with  insulated  gas-tight  fittings  to  contact 
point  at  K. 

Operation. — This  instrument  is  used  for  soft 
coal,  anthracite  or  coke,  and  for  oil  fuels.  For 
each  of  these  different  classes  the  charge  of  fuel 
and  chemicals  is  made  up  in  different  proportions, 
as  directed,  and  the  proper  constant,  as  determined 
by  the  inventor,  is  applied  for  the  calculation  of 
the  desired  result. 

To  prepare  the  cartridge  for  filling,  dry  all  the 
parts  perfectly  inside  and  out;  see  that  the  inner 
bottom  C  with  gasket  is  properly  seated,  screw  on 
the  outer  bell  E,  then  with  the  spanner  wheel  screw 
up  -firmly  the  outer  bottom  D  and  place  on  a  sheet 
of  white  paper. 

For  coals  under  test,  the  sample  is  in  all  cases 
prepared  by  grinding  in  a  mortar  and  passing 
through  a  100-mesh  sieve.  Coals  containing  more 
than  2£  or  3  per  cent  of  water  should  be  dried  be- 
fore testing.  In  such  cases  the  exact  charge  of  the 
commercially  dry  coal  is  weighed  out  and  dried  for 
an  hour  at  a  temperature  of  220° -230°  F.,  then 
transferred  to  the  cartridge.  One-half  gram  con-  FIG.  130. 
stitutes  the  charge  for  all  varieties  of  coal. 

The  apparatus  as  supplied  by  the  manufacturers  includes  the 
various  chemicals  that  are  to  be  used  for  testing  the  different 
varieties  of  fuel,  as  well  as  the  instruments  necessary  for  measuring 
or  weighing  them. 

Procedure  for  Soft  Coals. — One  full  measure  of  sodium  per- 
oxide, from  the  bottle  labelled  "  Chemical/'  is  put  in  the  cartridge 
and  the  charge  of  coal  added ;  then,  one  gram  of  finely  ground  chem- 


Hllll 


252  EXPERIMENTAL  ENGINEERING 

ically  pure  chlorate  of  potash,  from  the  bottle  labelled  "  Chlorate 
Mixture."  It  is  well  to  have  the  latter  follow  the  coal  and  thus 
clean  out  the  vessel  in  which  it  was  weighed. 

The  stem  and  top  B,  Fig.  130,  with  the  terminals  HI,  having  a 
loop  of  fine  ignition  wire  extending  about  an  inch  below,  are  put  in 
position,  and  the  cap  F  screwed  firmly  in  place.  Shake  vigorously 
to  thoroughly  mix  the  contents.  When  the  mixing  is  complete,  tap 
the  cartridge  lightly  to  settle  the  contents  and  to  shake  all  the  ma- 
terial from  the  upper  part  of  the  cylinder.  Put  on  the  spring  clips 
with  vanes.  The  cartridge  is  now  put  in  place,  the  can  with  water 
being  already  in  position.  Adjust  the  cover.  Insert  the  thermometer 
so  that  the  lower  end  of  bulb  will  be  about  midway  towards  the 
bottom  of  the  can,  place  the  pulley  on  the  stem  and  connect  with  the 
motor.  The  cartridge  should  turn  towards  the  right,  so  as  to  deflect 
the  currents  downward. 

After  about  three  minutes,  the  reading  of  the  thermometer  may 
be  taken,  giving  the  initial  temperature  of  the  water.  This  should, 
for  good  work,  be  about  3°  Fah.  below  the  temperature  of  the  atmos- 
phere. The  current  is  then  turned  on,  igniting  the  charge.  Com- 
bustion will  be  indicated  by  a  rapid  rising  of  the  temperature  of  the 
water,  which  should  reach  its  maximum  in  from  four  to  five  min- 
utes. During  the  combustion  the  revolving  of  the  cartridge  must 
be  kept  up  continuously. 

Calculation  of  Results. — The  initial  temperature  is  subtracted 
from  the  maximum  temperature  to  give  the  rise  in  temperature 
of  the  water.  From  this  is  subtracted  the  correction  factor  for 
the  heat  of  the  wire  and  chemical,  as  indicated  on  the  small  bottle 
of  chlorate  mixture.  The  remainder  is  multiplied  by  3115,  and  the 
product  thus  obtained  is  the  number  of  B.  T.  U.  in  a  pound  of  the 
fuel. 

The  factor  3115  is  deduced  as  follows:  The  water  used,  plus 
the  water  equivalent  of  the  calorimeter  is  2134  grams.  In  the  reac- 
tion that  takes  place  at  the  time  of  combustion,  73%  of  the  heat 
produced  is  due  to  the  combustion  of  the  coal,  and  27%  is  due  to  the 
heat  of  combination  of  CO 2  and  H20  with  the  chemical.  If  now 
^  gram  of  coal  causes  2134  grams  of  water  to  rise  r  degrees,  and  if 
only  73%  of  this  is  due  to  combustion,  then  0.73x2134x2x 
r=rise  in  temperature  that  will  result  from  the  combustion  of  one 


THE  SELECTION  AND  TESTING  OF  FUEL  253 

gram  of  the  coal.  0.73x2134x2  =  3115.  From  this  we  see  that 
one  gram  of  the  coal  will  raise  3115  grams  of  water  through  r 
degrees,  or  one  pound  of  the  coal  will  raise  3115  pounds  of  water 
through  r  degrees. 

After  using,  dismantle,  and  thoroughly  clean  the  instrument. 
Eemove  the  thermometer,  pulley,  and  cover;  then  take  out  the  can 
and  contents  entire,  so  that  the  lifting  out  of  the  cartridge  will  not 
drip  water  into  the  dry  parts  of  the  instrument.  Remove  the  spring 
clips  and  unscrew  the  ends.  It  is  better  to  loosen  the  bottom  D, 
Fig.  130,  and  unscrew  the  entire  bell  E  for  cleaning.  The  fused 
mass  is  easily  driven  out  at  the  bottom  by  aid  of  a  short  metal  rod, 
or  it  may  be  dissolved  out  by  immersing  the  cartridge  and  contents 
in  hot  water.  The  cartridge  and  ends,  when  rinsed  clean  and  thor- 
oughly dried,  will  be  ready  for  another  test. 

Procedure  for  Anthracite  or  Coke. — The  method  is  the  same  as 
for  soft  coal,  except  that  instead  of  1  gram  of  "  Chlorate  Mix- 
ture," H  grams  of  a  persulphate  mixture,  containing  2  parts  potas- 
sium persulphate  (KS04)  to  1  part  ammonium  persulphate 
(NH±SOt),  from  the  bottle  labelled  "  Special  Chemical "  is  substi- 
tuted. With  this  exception,  the  procedure  and  method  of  calculat- 
ing results  is  the  same  as  before.  The  correction  factor  for  the 
"  Special  Chemical "  and  fine  wire  is  marked  on  the  label  of  the 
"  Special  Chemical  "  bottle. 

Procedure  for  Oil  Fuels. — Prepare  a  small  light  15  cc.  weighing 
flask  with  perforated  cork  and  dropping  tube  with  common  rubber 
bulb  cap.  Fill  the  flask  about  f  full  of  oil  and  weigh  carefully. 
Place  in  the  cartridge  J  measure  of  ordinary  "  Chemical"  (sodium 
peroxide)  and  1^  grams,  exactly  weighed  out,  of  the  "  Special 
Chemical"  (persulphate  mixture).  Then,  by  means  of  the  drop- 
ping tube,  add  about  0.3  gram  (25-30  drops)  of  oil.  Add  one 
measure  of  ordinary  "  Chemical."  Screw  on  the  top,  shake  well, 
place  in  the  calorimeter,  and  ignite  as  usual.  Weigh  back  the  flask 
carefully  and  determine  the  amount  of  oil  taken  by  difference. 
Compute  the  result  by  formula  instead  of  using  a  factor,  thus : 
Correcting  as  before  for  the  wire  and  "  Special  Chemical,"  let 
r=the  corrected  rise  in  temperature;  then 

rX  0.73x2134         -D    m   TT  j     £    -i 

,    .,  .  -  =B.  T.  U.  per  pound  of  oil. 

wt.  oi  oil  in  grams 


254 


EXPERIMENTAL  ENGINEERING 


Junker's  Calorimeter. — This  is  an  apparatus  especially  designed 
for  gaseous  fuels.  It  is  shown  in  elevation  and  section  in  Figs. 
131  and  132.  The  principle  of  its  action  is  based  on  the  heating  of 
a  current  of  air  passing  around  a  jet  of  burning  gas  whose  heating 
value  is  to  be  determined.  A  combustion  chamber  A  has  a  burner 


FIG.  131. 

at  the  center  which  is  connected  to  the  source  of  supply  through  an 
accurate  gas  meter.  The  combustion  chamber  is  surrounded  by  a 
water  jacket  BB,  this  jacket  being  again  surrounded  by  a  closed 
annular  air  space  C,  through  which  the  air  cannot  circulate,  and 
fitted  for  the  purpose  of  preventing  loss  by  radiation.  The  nozzle 
D  in  the  center  of  the  container  E  is  connected  to  any  water  supply ; 
F  is  an  overflow  pipe,  the  discharge  from  which  should  be  visible, 


THE  SELECTION  AND  TESTING  OF  FUEL 


255 


but  need  not  be  measured,  as  this  water  does  not  form  part  of  the 
quantity  heated. 


FIG.  132. 


The  cold  water  enters  the  container  at  D,  passes  down  through 
G,  H,  and  leaves  the  jacket  at  L,  while  the  combustion  gases  enter 
at  M,  through  a  series  of  small  vertical  tubes  T,  in  the  water  jacket, 
pass  down  and  leave  at  N.  The  gas  and  water  move  in  opposite 


256  EXPERIMENTAL  ENGINEERING 

directions,  so  that  all  the  heat  is  transferred  to  the  water,  and  the 
waste  gases  leave  the  apparatus  approximately  at  atmospheric 
pressure.  The  temperature  of  the  water  entering  and  leaving  can 
be  read  by  thermometers  0  and  'P.  A  third  thermometer  gives  the 
temperature  of  the  products  of  combustion  from  the  gas  jet,  and  a 
fourth  that  of  the  gas  in  the  meter  Q.  The  water  produced  by  the 
combustion  of  the  hydrogen  in  the  burning  jet  and  the  oxygen  of 
the  air  forming  steam  is  condensed  in  the  calorimeter,  thus  giving 
up  its  latent  heat.  This  condensed  water  is  a  factor  in  the  determi- 
nation of  the  higher  or  lower  heating  value  of  the  gas,  consequently 
it  is  measured  by  running  it  into  the  graduate  K.  The  cocks 
should  be  opened  for  a  short  interval  before  a  test  in  order  to  clear 
the  pipes  of  air  and  obtain  water  only. 

Operation. — Water  is  run  into  D  until  it  passes  through  the 
jacket  and  flows  out  at  the  discharge  L.  The  gas  is  lighted  at 
the  burner,  inserted  in  the  calorimeter,  and  the  size  of  the  flame 
or  quantity  of  gas  passing  to  it  is  carefully  adjusted  by  the  gas 
supply  stop  cock.  The  air  for  combustion  is  supplied  from  the 
open  bottom,  as  shown  by  the  arrows.  The  products  of  combustion 
move  to  the  upper  part  of  the  calorimeter,  and  descend  through 
a  number  of  small  vertical  copper  tubes,  finally  emerging  at  N, 
and  go  to  waste  through  U.  The  heat  in  the  products  of  com- 
bustion is  absorbed  by  the  water  which  circulates  round  the  tubes 
as  it  passes  through  the  calorimeter. 

The  cock  V  (Fig.  131)  regulates  the  quantity  of  circulating  water 
which  is  measured  by  the  graduated  glass  X,  and  by  varying  the 
opening  of  V  before  getting  underway  for  the  test  the  difference 
of  temperature  between  inlet  and  outlet  is  approximately  deter- 
mined at  the  beginning.  This  adjustment  is  made  so  that  the 
circulating  water  during  the  passage  of  the  gases  absorbs  all  the 
heat  given  out,  and  the  products  of  combustion  at  release  are  prac- 
tically at  the  temperature  of  the  atmosphere. 

It  is  necessary  that  the  flow  of  circulating  water  should  be,  as 
nearly  as  possible,  constant.  In  order  to  accomplish  this,  the  water 
entering  at  D  supplies  the  tank  with  a  little  more  than  is  necessary, 
and  this  surplus  overflows  into  the  space  W  in  the  tank  and  thence 
into  the  drain  pipe.  Similarly  an  overflow  is  provided  at  Y.  By 


THE  SELECTION  AND  TESTING  OF  FUEL  257 

this  means  a  constant  head,  is  maintained,  and  a  constant  rate  of 
flow  obtained  through  the  calorimeter.  The  water,  in  its  passage 
at  entrance,  passes  through  the  thermometer  0,  from  which  the 
initial  temperature  is  obtained  and  the  final  temperature  by  the 
thermometer  P. 

Having  obtained  the  pounds  of  circulating  water  per  minute,  the 
rise  in  temperature  during  the  passage  through  the  calorimeter,  and 
the  number  of  cubic  feet  of  gas  used  per  minute,  the  calorific  value 
hf  of  the  fuel  is  obtained  from  the  formula 


where  W  —  pounds  of  circulating  water  measured, 

T—  difference  in  degrees  F.  of  the  initial  and  final  tem- 

perature of  the  circulating  water, 
(7  =  cubic  feet  of  gas  used. 

For  oils  a  special  burner  is  used. 

Example.  —  The  weight  of  the  circulating  water  used  was  seven 
pounds  per  minute,  the  rise  in  temperature  of  the  circulating  wrater 
was  30°  F.,  and  0.333  cubic  feet  of  gas  was  used  per  minute,  then 

calorific  value  =  ~       =630.6  B.  T.  IT.  per  cubic  foot. 


This  result  is  usually  termed  the  gross  calorific  value,  or  the 
higher  heating  value.  In  the  calorimeter  the  water  produced  in 
combustion  is  condensed  and  carried  off  as  already  explained 
through  pipe  R.  In  this  operation  it  gives  up  its  latent  heat,  and 
is  measured  in  the  cooling  water,  but  in  most  industrial  operations, 
such  as  the  performance  of  a  gas  engine,  the  water  formed  during 
combustion  passes  off  as  steam,  and  carries  with  it  the  latent  heat 
of  that  steam.  The  lower  heating  value,  or  what  is  sometimes 
called  the  available  calorific  value  is  equal  to  the  gross  value  minus 
the  latent  heat  of  steam  formed  per  cubic  foot  of  gas  at  the  tem- 
perature it  leaves  the  calorimeter.  As  the  temperature  of  the 
calorimeter  is  about  50°  F.,  the  total  heat  per  pound  is  equal  to 
1147-  (50-32)  =zll29  B.  T.  U.  per  pound  of  water.  Hence 
the  lower  heating  value  is  obtained  by  deducting  this  quantity  of 
heat  from  the  higher  heating  value  for  every  pound  of  water  pro- 
duced by  the  combustion  of  one  pound  of  gas. 
17 


258 


EXPERIMENTAL  ENGINEERING 


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THE  SELECTION  AND  TESTING  OF  FUEL  259 

There  is  a  difference  of  opinion  among  scientists  as  to  whether,  in 
a  calorimeter,  the  higher  or  lower  heating  value  should  be  taken. 
In  France  the  higher  heating  value  is  used,  while  in  Germany  the 
lower  value  is  always  taken,  consequently  in  any  reports  of  tests 
made,  the  condition  employed  should  always  be  stated. 

The  accompanying  table  from  an  efficiency  test  of  a  125-horse- 
power  gas  engine  by  C.  «EL  Robertson  shows  the  method  of  tabu- 
lating and  computing  results  by  means  of  a  Junker  calorimeter. 

Testing  Fuel  Oil. 

Navy  Specifications  for  Fuel  Oil. — (1)  Fuel  oil  shall  be  a  petro- 
leum oil  of  best  quality,  free  from  grit,  acid,  fibrous,  and  other 
foreign  matter  likely  to  clog  or  injure  the  burners  or  valves. 

(2)  The  unit  of  quantity  to  be  a  gallon  of  231  cubic  inches  at  a 
standard  temperature  -of  60°  F.    For  every  variation  of  temperature 
of  10°  F.  from  the  standard,  one-half  of  \%   shall  be  added  or 
deducted  from  the  measured  or  gaged  quantity  for  correction. 

(3)  Sulphur  in  the  oil  must  not  exceed  three-fourths  of  1%  by 
weight. 

(4)  Free  water  and  sediment  in  the  oil  shown  by  gasoline  test 
must  not  exceed  1%  by  volume.     The  gasoline  test  for  moisture 
shall  be  made  as  follows : 

(5)  Samples  taken  at  random  should  be  thoroughly  shaken  and 
mixed;  then  50  cc.  of  sample  placed  in  a  100  cm.  graduated  glass 
cylinder.    An  equal  quantity  of  not  less  than  68°  gasoline  should  be 
mixed  with  the  sample  in  the  graduated  glass,  the  combined  mix- 
ture of  oil  and  gasoline  should  then  be  thoroughly  shaken  and 
allowed  to  stand  not  less  than  six  hours,  when  percentage  of  water 
and  sediment  will  be  taken  by  the  inspector. 

(6)  The  oil  shall  not  flash  at  a  temperature  less  than  200° 
F.,  the  test  to  be  made  by  the  Abel  or  Pensky-Martin  closed-cup 
method. 

(7)  The  oil  shall  have  a  gravity  Baume  not  greater  than  30°  at 
60°  F.,  determined  from  an  average  sample. 

(8)  The  oil  shall  flow  freely  and  in  a  continuous  stream  through 
a  ^-inch  circular  hole  under  a  2-foot  head  at  a  temperature  of  40° 
F.     Oil  that  fails  to  flow  freely  and  in  the  required  quantities  to 


260 


EXPERIMENTAL  ENGINEERING 


THE  SELECTION  AND  TESTING  OF  FUEL  261 

pump  suctions,  pass  through  pumps,  piping,  and  burners  at  a 
temperature  of  40°  F.  may  be  rejected. 

(9)  The  oil  shall  have  a  calorific  value  not  under  144,000  B.  T. 
IT.  per  gallon,  to  be  taken  from  an  average  sample  or  samples  of 
the  product  as  delivered,  or  made  before  delivery.  In  determining 
this  value,  the  bomb  calorimeter  shall  be  used  to  determine  the 
B.  T.  U.  per  pound,  from  which  the  B.  T.  U.  per  gallon  shall  be 
calculated  by  using  8.331  pounds  of  distilled  water  per  gallon  at 
60°  F.  and  the  specific  gravity  of  the  oil  as  determined  by  the 
Baume  test  at  same  temperature.  Should  the  conditions  be  such 
that  oil  of  the  required  calorific  value  could  not  be  obtained,  oil  of 
a  less  calorific  value  may  be  accepted  at  a  reduction  of  1%  for  each 
1000  B.  T.  U.  or  fraction  exceeding  one-half  thereof;  but  no  oil 
having  less  than  135,000  B.  T.  U.  per  gallon  will  be  accepted. 

Each  vessel  that  burns  oil  and  all  oil  supply  stations  are  pro- 
vided with  a  portable  test  outfit  as  illustrated  in  Fig.  133.  This 
has  instruments  for  determining  the  flash  point,  percentage  of 
water  and  sediment,  and  specific  gravity.  Samples  are  sent  to  a 
laboratory  for  the  determination  of  the  percentage  of  sulphur  and 
the  heating  value. 

The  following  instructions  cover  the  use  of  the  standard  test 
outfit : 

Instructions  for  Testing  Fuel  Oil  for  IT.  S.  Navy. 

The  Pensky-Martens  Apparatus  for  Flash  Point:     Description. 

Referring  to  Fig.  134. — E  is  the  oil  container,  which  is  placed  in  a 
metal  heating  vessel  H,  provided  with  a  mantle  L  in  order  to  pro- 
tect H  from  loss  of  heat  by  radiation.  The  oil  cup  E  is  closed  by  a 
tightly  fitting  lid  (shown  in  plan  2).  Through  the  center  of  the 
lid  passes  a  shaft  carrying  the  stirring  arrangement,  which  is 
worked  through  a  flexible  connection  by  means  of  the  handle  J. 
In  another  opening  of  the  cover  is  fixed  a  thermometer.  The  lid 
is  perforated  with  several  orifices,  which  are  left  open  or  covered, 
as  the  case  may  be,  by  a  sliding  cover.  This  can  be  rotated  by  turn- 
ing the  vertical  spindle  with  milled  head  G.  By  turning  G,  an 
opening  of  the  slide  can  be  made  to  coincide  with  an  orifice  in  the 
cover,  and  simultaneously  a  jet  of  flame  P,  from  a  very  small  spirit 


262 


EXPERIMENTAL  ENGINEERING 


lamp,  is  tilted  on  the  surface  of  the  oil.    This  contrivance  is  shown 
on  a  larger  scale  in  plan  2. 

Operation. — All  water  which  is  contained  in  the  oil  must  be  re- 
moved before  testing  for  flash  point  by  filtering  it  through  one  of 
the  small  felt  niters  and  funnels  contained  in  the  outfit.  When 


FIG.  134. 

the  sample  is  prepared  for  test,  the  oil  cup  is  filled  up  to  the  mark, 
the  cover  is  fixed  and  the  oil  heated  rapidly  until  its  temperature 
reaches  a  point  about  50°  F.  below  the  expected  flash  point.  The 
wire  gage  screen,  shown  in  Fig.  134,  is  then  placed  in  position  and 
the  rate  of  rise  in  temperature  is  thus  reduced  to  about  5°  a  minute. 
Handle  J  is  turned  slowly  and  continuously  for  stirring.  From 


THE  SELECTION  AND  TESTING  OF  FUEL  263 

time  to  time  the  milled  head  G  is  turned,,  opening  the  shutter  at 
top  of  the  cup  and  tilting  into  it  the  flame  P.  This  is  done  at  in- 
tervals of  5°  F.  rise  in  temperature  until  near  the  probable  flash 
point  when  the  intervals  are  made  2°  F.  When  the  flash  point  is 
reached  there  will  be  a  slight  explosion  when  the  flame  is  tilted 
down. 

A  sample  can  only  be  used  for  one  test,,  since  the  more  volatile 
products  are  driven  off  and  subsequent  tests  would  show  a  higher 
flash  point. 

The  Fire  Test. — This  is  the  temperature  at  which  the  oil  will 
give  off  vapors  which  when  ignited  will  burn  continuously.  It  is 
maae  by  continuing  to  heat  the  oil  after  the  flash  point  is  estab- 
lished. In  a  closed  testing  apparatus  the  cover  is  removed  for  this 
test,  the  thermometer  remaining  in  place.  The  flame  is  extin- 
guished by  putting  on  the  cover. 

Test  for  Determining  Water  and  Sediment. — The  outfit  contains 
a  graduated  glass  cylinder,  as  shown,  having  a  small  stem  at  bottom 
of  3  cc.  capacity.  Fifty  cc.  of  the  oil  under  test  is  placed  in  the 
cylinder  and  an  equal  quantity  of  gasoline  or  kerosene  added. 
The  whole  is  then  shaken  thoroughly  and  allowed  to  stand  for  at 
least  two  hours.  All  the  oil  and  sediment  will  then  be  found  to 
have  settled  in  the  narrow  stem  where  it  can  be  measured.  If 
bubbles  are  found  to  be  adhering  to  the  glass  they  are  removed  with 
a  thin  wire  agitator. 

Each  cc.  of  water  and  sediment  found  in  the  stem  will  represent 
2  per  cent  in  the  sample  tested. 

Specific  Gravity. — A  sample  of  the  oil  is  placed  in  the  graduated 
glass  jar,  shown  in  Fig.  133,  and  a  hydrometer  slowly  sunk  into  it. 
Care  must  be  taken  riot  to  plunge  the  hydrometer  deeper  than  it 
will  float  as  this  will  make  an  accurate  reading  impossible.  After 
reading  the  hydrometer  it  is  removed  and  the  temperature  taken. 
By  means  of  a  correction  table  the  specific  gravity  is  reduced  to 
60°  F.,  which  is  the  standard  for  comparison. 

Commercially  the  specific  gravity  of  an  oil  in  the  United  States 
is  usually  given  according  to  the  Baume  scale,  an  arbitrary  stand- 
ard whose  value  at  various  points  is  as  follows.  The  weight  per 
gallon  is  given  at  60°  F. : 


264  EXPERIMENTAL  ENGINEERING 

10°    Baume  =  s.  g.  1.000  =  8.331  pounds  per  gal. 

15°  "  =  "  .967  =  8.056  "  "  " 

20°  "  =  "  .936  =  7.798  "  "  " 

25°  "  =  "  .907  =  7.556  "  "  " 

30°  "  =  "  .880  =  7.331  "  "  " 

35°  "  =  "  .854  =  7.115  "  "  " 

40°  "  =  "  .830  =  6.915  "  "  " 

45°  "  =  "  .807  =  6.723  "  "  " 

50°  "  =  "  .785  =  6.540  "  "  " 

55°  "  =  "  .765  =  6.373  "  "  " 

60°  '"  =  "  .745  =  6.206  "  "  " 

Other  Oils  for  Burning. — In  addition  to  fuel  oil,  there  is  carried 
on  board  our  naval  vessels  kerosene  or  mineral  oil  for  use  in  lamps 
and  as  fuel  in  some  of  the  internal  combustion  engines  for  motor 
boats,  and  gasoline  which  is  the  fuel  most  commonly  employed  in 
motor-boat  engines.  Lard  oil,  after  it  had  been  supplanted  as  a 
lubricant  by  compounded  oils,  was  for  several  years  carried  for 
use  in  oil  lamps.  This  has  now  been  wholly  dispensed  with. 
Hand  lamps  in  the  engineer  department  are  fitted  to  burn  vaclite, 
a  very  heavy  paraffine  oil  which  is  solid  at  ordinary  temperatures. 
This  material  is  usually  purchased  under  its  proprietary  name. 
Other  lamps  are  now  fitted  to  burn  kerosene. 

Specifications  for  Mineral  Oil  (Kerosene). — (1)  Samples  of 
each  lot,  taken  at  random,  will  be  tested  photometrically  after 
burning  one  hour  in  lamps  fitted  with  No.  1  hinge  burners,  Marcy's 
patent,  the  standard  employed  being  a  standard  Hoefner  lamp. 
After  burning  five  hours  longer,  the  lamps  will  be  again  tested  to 
determine  any  change  in  the  intensity  of  the  light.  The  flame 
must  be  of  at  least  6  candlepower  and  must  show  no  material  change 
in  intensity  during  the  five-hour  interval. 

(2)  The  samples  must  show  a  flash  test  of  not  less  than  115°  F. 
and  a  fire  test  of  not  less  than  140°  F.    The  flash  and  fire  tests  are 
to  be  conducted  in  a  closed  tester  of  the  "  Tagliabue  "  type. 

(3)  The  oil  will  be  tested  for  the  presence  of  a  free  acid.  Litmus 
paper  immersed  in  the  oil  for  five  hours  must  remain  unchanged. 

(4)  The  specific  gravity  must  not  be  greater  than  0.793  at  a 
temperature  of  60°  F. ;  to  be  purchased  and  inspected  by  weight. 

(5)  The  oil  must  burn  steadily  and  clearly,  in  a  suitable  lamp, 


THE  SELECTION  AND  TESTING  OF  FUEL  265 

without  smoking  and  with  a  minimum  incrustation  of  the  wick, 
for  a  period  of  at  least  seventy-two  hours. 

The  Tagliabue  apparatus  for  taking  the  flash  and  fire  test  under 
these  specifications  is  similar  to  the  New  York  State  Board  of 
Health  Tester  shown  in  Fig.  121,  except  that  the  cup  has  a  metal 
cover  with  a  hole  to  which  a  match  is  applied  in  making  a  test. 
A  slide  over  this  opening  is  kept  closed  except  when  applying  the 
match. 

Specifications  for  Gasoline  for  Use  in  II.  S.  Navy  Motor 
Launches. — (1)  To  be  a  high  grade,  refined,  gasoline,  free  from  all 
impurities. 

(2)  Inspection. — Before    acceptance    the    gasoline    will   be    in- 
spected.    Samples   of   each  lot  will  be  taken  at  random;  these 
samples  will  be  well  mixed  in  a  clean,  closed  vessel,  and  a  sample 
for  test  taken  from  this  mixture. 

(3)  Test. — 100  cc.  will  be  taken  as  a  test  sample.    This  amount 
will  be  distilled  in  an  Engler  apparatus  at  a  rate  of  not  less  than 
10  cc.  per  minute. 

(a)  Boiling  point  must  not  be  above  135°  F. 

(b)  Not  less  than  10%  shall  distill  over  below  150°  F. 

(c)  At  least  50%  of  the  sample  must  distill  over  below  200°  F. 

(d)  One  hundred  per  cent  must  distill  over  below  310°  F. 

(e)  Not  less  than  96%  of  the  liquid  will  be  recovered  from  the 
distillation. 

(4)  Five  cubic  centimeters  of  the  sample  when  poured  over  a 
sheet  of  white  paper  shall  evaporate  completely  without  leaving  any 
stain. 

(5)  Apparatus. — The     apparatus     used     for     distillation     and 
method  of  conducting  the  test  shall  be  as  follows :    The  apparatus 
shall  consist  of  a  4-ounce  Engler  flask  with  outlet  high  on  neck. 
The  top  of  the  thermometer  bulb  shall  be  opposite  the  bottom  of  the 
outlet  tube.     The  condenser  shall  be  a  standard  20-inch  Liebig 
type  of  condenser.     The   boiling  point  will  be  the   temperature 
shown  by  the  thermometer  when  the  first  drop  of  the  condensed 
liquid  falls  from  the  end  of  the  condenser  into  the  receiving  flask. 
The  distillation  shall  be  pushed  to  completion,  at  which  time  the 
bottom  of  the  flask  will  be  dry.   The  end  point  at  this  time  will  be 
indicated  by  a  small  flask  or  puff  of  smoke. 


CHAPTEE  XI. 
FLUE  GAS  ANALYSIS. 

When  coal  is  burned  in  the  furnace  of  a  boiler,  the  products  of 
combustion  are,  for  the  most  part,  carbon  dioxide  (C02),  carbon 
monoxide  (CO),  free  oxygen,  and  nitrogen.  A  small  percentage  of 
steam  (H20)  is  also  present,  resulting  from  the  combustion  of  such 
portion  of  hydrogen  as  is  in  the  coal.  If  it  were  possible  to  supply 
air  in  such  quantity  that  the  carbon  in  the  coal  would  be  completely 
burned  to  C02,  and  no  more,  and,  furthermore,  if  it  were  possible 
to  completely  utilize  all  this  air,  combustion  of  maximum  efficiency 
would  be  obtained.  The  C02  in  the  resulting  products  of  combus- 
tion would  then  be  about  21%  and  there  would  be  no  free  oxygen 
or  carbon  monoxide  present.  In  practice,  in  order  to  obtain  the 
best  possible  results,  a  much  larger  quantity  of  air  must  be  supplied, 
and  as  this  quantity  is  increased  the  percentage  of  C02  given  off  is 
reduced.  The  efficiency  of  combustion  is  correspondingly  reduced 
on  account  of  the  great  quantity  of  heat  lost  with  the  additional 
volume  of  gases  through  the  chimney.  If,  on  the  other  hand,  an 
insufficient  quantity  of  air  should  be  supplied,  the  percentage  of  CO 
will  be  increased  and  the  percentage  of  C02  correspondingly  re- 
duced, showing  a  loss  of  efficiency  from  incomplete  combustion. 

The  percentage  of  C02  present  in  the  flue  gases  is  thus  seen 
to  measure  approximately  the  efficiency  of  combustion.  Where 
21%  CO 2  represents  perfect  efficiency,  15%  C02  represents  a  loss 
of  12%'  in  efficiency  of  combustion.  Fifteen  per  cent  is  about  the 
maximum  proportion  of  C02  that  it  is  possible  to  obtain,  the  usual 
figure  running  down  to  7%  or  8%,  representing  a  loss  of  20%  to 
21%  in  efficiency.  It  becomes  evident  then  that  an  apparatus  for 
measuring  the  percentage  of  C02  in  the  products  of  combustion, 
affords  a  valuable  means  of  checking  losses  from  this  cause. 

The  Orsatt-Muencke  Apparatus. — This  is  shown  in  Fig.  135  in 
which  B  is  a  measuring  tube,  surrounded  by  a  water  jacket  and 
connected  to  a  levelling  bottle  K.  The  upper  end  of  B  is  connected 


FLUE  GAS  ANALYSIS 


267 


by  a  pipe  to  a  nozzle  F  from  which  a  hose  connection  leads  to  the 
sampling  tube  for  obtaining  the  gas  that  is  to  be  tested.  Three 
U-shaped  reagent  bottles  A,  A',  and  A"  are  each  connected  at  one 
end  by  a  short  rubber  tube  with  stop  cock  to  the  pipe  connecting 
B  with  F.  The  other  end  is  open  to  the  atmosphere. 


FIG.  135. 


The  reagent  bottles  are  about  half  filled  with  reagents  as  follows : 

(1)  Bottle  A  with  potassic  hydrate  to  absorb  C02.     This  is  a 
solution  in  distilled  water  of  from  3  to  5%  of  white  caustic  potash, 
which  comes  in  sticks. 

(2)  Bottle   A!   with   potassic   pyrogallate   to   absorb   the   free 
oxygen.     This  reagent  is  prepared  by  mixing  a  strong  solution  of 


268  EXPERIMENTAL  ENGINEERING 

potassic  hydrate  with  3%  solution  of  pyrogallic  acid.  It  will  take 
about  five  minutes  to  absorb  the  oxygen. 

(3)  Bottle  A"  with  cuprous  chloride  solution  in  concentrated 
hydrochloric  acid  to  absorb  the  CO.  This  solution  keeps  best  in  a 
bottle  containing  a  few  pieces  of  clean  copper  wire.  The  absorp- 
tion of  CO  takes  longer  than  that  of  0. 

Operation. — The  cocks  on  the  reagent  bottles  having  been  closed 
and  the  cock  on  F  opened,  the  bottle  K  is  partially  filled  with 
water,  the  water  being  allowed  to  run  in  and  fill  the  measuring 
tube  B.  By  lowering  K,  gas  is  drawn  in  through  F  filling  B. 
Eaising  and  lowering  K  several  times  the  apparatus  is  cleared  of 
air.  Finally  100  cc.  of  gas  is  drawn  into  B  and  the  cock  on  F 
closed.  Then  open  the  cock  on  A  and  allow  the  reagent  in  it  to 
absorb  the  C02  by  raising  and  lowering  K  alternately  several  times. 
The  last  time  the  reagent  must  be  allowed  to  fill  the  leg  next  to 
the  measuring  tube  completely.  In  order  to  be  sure  that  the 
absorption  of  C02  is  complete,  the  test  should  be  repeated  until  the 
last  readings  of  the  measuring  tube  agree  within  0.1%.  The  dif- 
ference between  the  last  reading  and  the  100  cc.  originally  drawn 
into  B  gives  the  volume  of  C02  absorbed  which  represents  the 
percentage  of  C02  in  the  gas. 

Similarly  using  reagent  A'  the  0  is  absorbed,  after  which  using 
A"  the  CO  is  eliminated.  The  volume  in  each  case  represents  the 
percentage  present  in  the  original  100  cc.  For  these  gases  the  last 
readings  of  the  measuring  tube  must  agree  exactly. 

The  remainder,  after  the  C02,  0  and  CO  are  absorbed,  is  classed 
as  nitrogen.  When  transferring  the  gas  during  these  operations 
care  must  be  taken  not  to  allow  any  of  the  reagents  to  get  into 
the  measuring  tube,  as  the  water  in  the  bottle  must  then  be  changed. 
A  small  quantity  of  water  running  into  the  reagent  bottles  during 
a  transfer  will  do  no  harm. 

A  complete  analysis  will  require  about  twenty  minutes.  Care 
must  be  taken  to  have  the  water  in  levelling  bottle  and  reagents 
at  the  approximate  temperature  of  the  room,  so  that  while  the 
analysis  is  in  progress  there  will  be  no  change  in  the  temperature 
of  the  gas  and  the  volumes  absorbed  will  correctly  represent  the 
percentages  of  each  constituent  by  volume. 


FLUE  GAS  ANALYSIS  269 

Calculations  from  Results  of  Analysis.  —  The  weight  of  dry  gases 
per  pound  of  fuel  as  fired,  is  calculated  from  the  analyses  of  the 
gases  and  the  fuel  and  from  that  the  number  of  pounds  of  dry  air 
passing  through  the  furnace  per  pound  of  fuel  is  found.  An  ap- 
proximate heat  balance  can  then  be  compiled,  showing  the  losses  in 
the  heating  value  of  the  fuel  due  to  the  several  causes.  The  heat 
units  utilized  are  obtained  from  the  results  of  the  evaporative  test 
of  the  boiler.  In  order  to  make  such  results  comparative,  the  com- 
putations are  based  on  the  pound  of  combustible. 

Example.—  The  gas  analysis  shows  C02,  12.7;  0,  5.7;  CO,  0.5, 
and  1\,  81.1  by  difference.  The  fuel  analysis  shows  C,  83.5;  H, 
4.8;  0,  3.2;  N",  1.2;  S,  0.5;  moisture,  1.5;  and  ash  5.3.  The 
calorific  value  of  one  pound  of  dry  coal  was  found  to  be  14,580 
B.  T.  U.  by  coal  calorimeter. 

The  analysis  of  the  coal,  referred  to  combustible,  i.  e.f  coal  less 
the  ash,  would  then  be,  in  per  cent,  88.2  C  (83.5x100-^-94.7), 
5.1  H,  3.4  0,  1.2  N",  0.5  S,  and  1.6  moisture.  The  calorific  value 
of  one  pound  of  dry  combustible  was  found  to  be  15,640  B.  T.  U. 

By  Avogadro's  hypothesis,  the  weight  of  a  gaseous  compound  is 
equal  to  its  molecular  weight,  referred  to  hydrogen  as  unity.  The 
chemical  equivalent  by  volume  of  CO  and  C02  is  2,  and  of  0  and  N 
is  1,  referred  to  hydrogen  as  unity,  or,  the  molecular  weights  of 
H,  0  and  N  are  twice  that  of  their  atomic  weights.  The  weight 
of  dry  gases  will,  therefore,  be  the  percentage  of  each  gas  found  in 
the  analysis  multiplied  by  its  molecular  weight,  or 
Poundsof  drygas=  %C02  x  44+  %02  X  32  +  %CO  X  28  +  %N2  X  28. 

The  pounds  of  dry  gas,  per  pound  of  carbon,  will  then  be  this 
amount  divided  by  the  product  of  the  atomic  weight  of  carbon  and 
the  sum  of  the  percentages  of  the  carbon  bearing  gases.  This  is 
deduced  as  follows  : 

Weight  of  gases  containing  carbon  =  C02X  44  +  CO  x28. 

Since  -fa  of  the  C02  and  -f-  of  the  CO  is  carbon,  therefore, 
3xC02x44        3xCOx28 

Letting  the  symbols  represent  the  percentages,  by  volume, 
Pounds  of  dry  gas  per  pound  of  carbon  burned 


12(C02  +  CO)  3(C02  +  CO) 


270  EXPEEIMENTAL    ENGINEERING 

Substituting  the  percentage  values  from  the  gas  analysis  given 
above,  we  get, 

Dry  gas  per  pound  of  carbon 


The  number  of  pounds  of  dry  gas  per  pound  of  combustible 
=  pounds  of  gas  per  pound  of  carbon  multiplied  by  the  percentage 
of  carbon  (in  decimals)  in  the  combustible. 

Or,  in  this  case, 

Dry  gas  per  pound  of  combustible  =  19.  lx.  882  =  16.  85  pounds. 

The  number  of  pounds  of  dry  gas  per  pound  of  coal  as  fired 
=  pounds  of  gas  per  pound  of  carbon  multiplied  by  percentage  of 
carbon  (in  decimals)  in  the  coal. 

The  gas  analysis  accounts  for  the  carbon  only,  and  we  must, 
therefore,  add  the  H20  in  the  gases,  formed  by  evaporating  the 
moisture  and  by  burning  the  H  in  the  coal.  The  latter  we  find 
on  the  same  principle  as  above,  and  the  former,  from  the  coal 
analysis.  Hence, 

48x9 

H20  from  hydrogen  in  coal  =    '  =.52  pound. 

oo.5 

H20  from  moisture  in  coal  =  .  053  x.  835  =  .04  pound. 

.56  pound. 

Or,  the  total  weight  of  gases  per  pound  of  carbon=19.1  +  .56 
=  19.66  pounds;  per  pound  of  combustible  =  16.85  +  .56  =  17.41 
pounds  ;  and  per  pound  of  coal  as  fired  =  19.66  X  .835  =  16.42  pounds. 

The  quantity  of  air  which  passed  through  the  furnace  for  each 
pound  of  combustible  is,  therefore,  17.4  —  1  =  16.4  pounds.  The 
air  per  pound  of  coal  is  only  approximately  one  pound  less  than 
the  gas  per  pound  of  coal. 

Loss  by  Heat  of  Gases.  —  Suppose  that  the  temperature  of  the 
gases  in  the  uptake  or  smoke  pipe  was  590°,  and  that  of  the  ex- 
ternal air,  75°  F.  For  all  practical  purposes,  and  in  view  of  the 
approximate  results  which  can  be  obtained  by  the  present  state 
of  the  art  of  gas  analysis,  the  average  specific  heat  of  the  dry  gases 
may  be  taken  as  .24,  and  of  the  dry  gases  including  the  H20,  as 
.246. 


FLUE  GAS  ANALYSIS  271 

The  rise  in  temperature  is  515°  F.  As  there  were  17.41  pounds 
of  gases  for  each  pound  of  combustible,  the  sensible  heat  loss  was, 

17.41  X.  246x515  =  2204  heat  units  per  pound  of  combustible  (1). 

Loss  Due  to  Latent  Heat  in  H20.  —  The  loss  of  sensible  heat  in 
the  steam  gas  has  been  accounted  for  in  the  above  calculation,  but, 
in  addition,  there  is  the  loss  of  heat  rendered  latent  by  changing 
the  H20,  formed  from  the  H  and  H20  in  the  coal,  from  water  into 
steam.  The  latent  heat  of  one  pound  of  steam  under  atmospheric 
pressure  is  965.8.  It  was  found  above  that  .56  pound  of  H20  gas 
was  evolved  from  the  coal.  The  loss  is,  therefore, 

.06x965.8  =  541  heat  units  per  pound  of  combustible   (2). 

•  Loss  Due  to  Incomplete  Combustion.  —  As  we  have  found  before, 
the  weight  of  the  carbon  in  the  gases  is  12(C02-1-CO).  The 
perfect  or  complete  combustion  of  this  total  carbon  would  have 
given  12(C02  +  CO)  x  14,600  heat  units—a.  But  the  combustion 
of  the  carbon,  as  shown  by  the  gas  analysis,  was  only  partially 
complete,  and  the  heat  generated  was,  therefore,  only  12C02  X  14,600 
+  1200x4400  units  =  6.  The  difference  between  the  two  will 
give  the  loss  in  heat  units  due  to  the  incomplete  combustion,  or, 
Loss  =  a  —  b  =  1200x10,200  heat  units,  or  in  per  cent  of  a, 

1200x10,200x100       00x10,200x100  ,     .       , 

12(C02  +  CO)  -CO.  +  CO      ~  PCT  P°Und  °f  Carb°n- 

And  per  pound  of  combustible, 

T       _  00x10,200       %C  in  combustible 
C02  +  C0    X  100 

Substituting  values  from  the  above  gas  and  chemical  analyses, 
we  get  loss  due  to  incomplete  combustion,  per  pound  of  combustible 

(3). 


Suppose  that  the  results  of  the  evaporative  test  of  the  boiler 
gave  11.6  pounds  as  the  equivalent  evaporation  from  and  at  212°  F. 
per  pound  of  combustible.  Then, 

11.6x965.8  =  11,203  heat  units  absorbed  by  boiler  (4). 


272  EXPERIMENTAL  ENGINEERING 

From  this  and  the  losses  computed  above,  we  can  make  up  a 
heat  balance  which  will  show  the  approximate  distribution  of  the 
heating  value  of  one  pound  of  the  combustible. 

Calorific  value  of  the  combustible 15,640  heat  units. 

Absorbed  by  the  boiler 11,203 

Loss  due  to  sensible  heat  in  waste 

gases    2,206 

Loss   due   to   latent  heat   in   steam 

gas    , 541 

Loss  due  to  incomplete  combustion.  .  341 
Other  losses,  due  to  radiation,  etc., 

by  difference    1,349 


15,640 

These  values  are  frequently  expressed  in  per  cent  of  the  calo- 
rific value  of  the  combustible. 

Apparatus  for  Determining  C02  Alone. — A  complete  analysis  of 
the  flue  gas  affords  most  valuable  information  and  is  made  a  part 
of  all  complete  boiler  tests.  For  the  daily  routine  in  a  boiler  plant 
complete  analyses  are  unnecessary  and  such  work  may  be  restricted 
to  the  determination  of  the  percentage  of  C02  alone.  This  in  itself 
affords  a  complete  index  to  the  character  of  the  firing  and  discloses 
any  waste  due  to  an  excessive  or  insufficient  supply  of  air. 

The  Hays  C02  Apparatus. — This  is  a  modified  and  simplified 
form  of  the  apparatus  described  on  page  267.  It  is  used  for  the 
determination  of  C02  alone,  and  is  supplied  to  many  of  the  vessels 
of  the  navy.  It  is  shown  in  Fig.  136  and  the  method  of  operation 
is  described  by  the  manufacturer  as  follows : 

Eeferring  to  Fig.  136. 

Sample  of  gas  is  first  measured  in  the  burette  A.  It  is  then 
passed  into  the  pipette  B  where  it  comes  in  contact  with  an  ab- 
sorbent solution.  It  is  next  returned  to  the  burette  and  remeas- 
ured.  The  shrinkage  represents  the  percentage  of  the  gas  absorbed. 

The  burette  A  is  surrounded  by  a  water  jacket  Al  and  suspended 
on  piano-wire  springs.  A  leveling  bottle,  C,  is  connected  with 
bottom  of  burette  and  is  filled  with  water,  brine,  or  solution  of 
glycerine  and  water  as  preferred.  Absorbent  liquid  is  introduced 


FLUE  GAS  ANALYSIS 


273 


into  B  through  the  funnel  E.    Pipette  holds  sufficient  potash  for  500 
C02  determinations. 

To  operate  the  instrument  hang  upon  any  convenient  nail  at  T. 
Remove  stopper  from  leveling  bottle  and  also  stopper  8.     Open 


FIG.  136. 


pinch  cock  K  and  raise  leveling  bottle  until  liquid  entirely  fills  the 
burette.  Return  leveling  bottle  to  its  compartment;  connect  hose 
N  with  a  piece  of  gas  pipe  and  insert  same  into  breeching  or  other 
point  from  which  it  is  desired  to  draw  the  gas  to  be  analyzed.  Open 
pinch  cock  Q  and  pump  the  aspirator  bulb.  Gas  enters  the  burette 
and  bubbles  out  through  the  leveling  bottle.  Next  open  pinch  cock 
18 


274  EXPERIMENTAL  ENGINEERING 

K  and  slowly  raise  leveling  bottle  until  the  liquid  reaches  the  zero 
mark  on  the  burette.  Gas  is  passed  back  and  forth  between  burette 
and  pipette  by  opening  pinch  cock  L  and  manipulating  the  leveling 
bottle. 

Any  absorbable  gas  can  be  determined  with  this  instrument,  by 
changing  the  solutions  in  the  absorption  pipette. 

In  determining  0  and  CO  in  boiler  furnace  practice  it  is  usually 
desired  to  know  the  averages  of  these  gases  from  a  large  number  of 
samples.  The  residue  after  each  C02  absorption  is  discharged  into 
the  sampling  bottle  furnished  with  the  instrument.  One  analysis 
for  0  and  CO  accordingly  gives  the  averages  for  these  gases  on  all 
the  samples  submitted  to  C02  absorption. 

An  analysis  for  C02  can  be  made  every  two  minutes  with  this 
instrument  and  the  average  0  and  CO  determined  in  10  minutes  on 
any  desired  number  of  gas  samples. 

The  introduction  of  this  apparatus  in  our  naval  vessels  resulted 
in  an  immediate  increase  in  the  efficiency  of  firing  with  a  marked 
decrease  in  coal  consumption. 

The  Sarco  Automatic  CO,  Recorder. — Eef erring  to  Fig.  137, 
the  power  required  to  drive  this  apparatus  is  derived  from  the  main 
flue  or  chimney  in  the  following  manner :  A  water  tank  A,  of  an- 
nular section  is  filled  with  water,  forming  a  seal  for  the  gas  tank  C. 
This  gas  tank  is  balanced  by  a  weight  D,  suspended  by  a  cord,  pass- 
ing over  the  pulley  E.  F  is  a  tube  which  passes  under  A  and  up 
through  the  inner  compartment  to  the  nozzle  G,  which  is  above  the 
level  of  the  water.  This  tube  is  connected  to  the  main  flue  or 
chimney  at  H,  through  ordinary  tubing,  and  the  draught  by  ex- 
hausting the  gas  tank  0,  causes  the  same  to  sink  downward  into  A. 

This  motion  continues  until  C  reaches  its  lowest  point,  when  the 
stop  J±  strikes  a  lever,  automatically  opening  the  valve  /.  This 
admits  air  to  C,  which  then  rises  until  the  stop  J2  strikes  the  lever, 
closing  valve  I,  when  the  whole  operation  is  repeated.  This  move- 
ment continues,  furnishing  the  power  necessary  for  the  operation 
of  the  apparatus,  so  long  as  the  communication  with  the  flue  or 
chimney,  through  H,  is  uninterrupted.  A  pinch  valve  L  affords  a 
means  of  regulating  the  speed  of  operation. 


FLUE  GAS  ANALYSIS 


275 


FIG.  137. 


276 


EXPERIMENTAL  ENGINEERING 


The  Gas  Pumps  and  Valves. — The  power  thus  obtained  is  utilized 
to  work  two  plungers  (Fig.  138)  attached  to  the  side  of  the  motor 
and  connected  to  the  large  pulley  by  wires  running  over  two  small 
pulleys,  as  shown  in  Fig.  137.  These  plungers,  or  pumps,  A^  and 
A  2,  are  themselves  small  gas  tanks,  which 
dip  into  an  oil  seal  contained  in  the  tanks 
B!  and  j?2,  the  suction  tubes  to  A^  and  A2 
going  down  through  the  center.  To  these 
tubes  are  attached  two  sets  of  valves  C19 
C2,  and  Dlt  D2,  so  constructed  as  to  pre- 
vent the  return  of  any  gases  that  may 
enter  through  overcoming  the  small  re- 
sistance offered  by  the  glycerine  with 
which  they  are  partly  filled.  The  two 
plungers  move  up  and  down  alternately, 
one  sucking  gases  into  the  valves  while  the 
other  is  pressing  the  same  out  through  the 
outlet  E  and  into  the  registering  cabinet, 
a  diagram  of  which  is  shown  in  Fig.  139. 
A  continuous  flow  of  gases  is  secured  by 
this  arrangement,  air  bubbles  showing  at 
the  seal  F,  in  case  the  flow  should  in  any 
way  be  interrupted.  To  the  lower  outlet 
of  the  pump  valves  is  attached  an  escape 
G,  through  which  the  surplus  flue  gases, 
not  required  for  analysis,  pass  out  into  the 
atmosphere. 

The  Analyzing  and  Recording  Appara- 
tus.— Coming  from  the  pumps,  the  flue 
gases  enter  the  registering  cabinet  (Fig. 

139)  at  H,  pass  down  tube  I,  and  into  vessels  J"±  and  J2.  These  ves- 
sels are  in  communication  with  a  bottle  K  through  the  tube  L. 
Bottle  K  contains  a  mixture  of  glycerine  and  water.  It  is  attached 
to  the  weight  D  (Fig.  137),  and  is  carried  up  and  down  regularly 
with  it. 

On  the  up  stroke  the  liquid  in  K  rises  in  tube  L  and  seeks  its 
level  in  vessels  J^  and  J2,  into  which  the  flue  gas  is  being  pumped. 


Dl 


FLUE  GAS  ANALYSIS 


277 


FIG.  139. 


278  EXPERIMENTAL  ENGINEERING 

As  soon  as  the  liquid  covers  the  end  of  tube  /,  where  it  enters 
J19  the  flow  of  gas  into  J19  J2,  is  stopped.  Part  of  the  contained 
gases  then  escape  through  the  inner  tube  J3  into  the  atmosphere 
and  when  this  outlet  is  sealed  by  the  liquid  rising  further,  exactly 
100  cubic  centimeters  of  flue  gases  are  tapped  in  Jly  J2.  This 
quantity  is  gradually  forced  through  the  small  curved  tube  M  and 
brought  into  contact  with  a  solution  of  caustic  potash,  with  which 
vessel  N  is  filled  to  the  mark  ras.  The  pressure  of  the  gas  on  the 
surface  of  the  potash  displaces  same  in  N,  forcing  it  up  into  vessel 
0.  The  air  which  is  thus  displaced  in  0  passes  under  cylinder  P, 
which  is  suspended  by  a  silk  cord  and  accurately  counterbalanced. 

The  slight  pressure  thus  created  causes  lever  Q  to  swing  upwards, 
carrying  with  it  pen  R,  which  is  attached  to  the  end  of  the  lever. 
This  pen  rests  against  a  circular  drum  fitted  with  clockwork  and 
makes  a  continuous  record  on  a  chart  that  is  fitted  on  the  drum. 
This  chart  is  calibrated  in  terms  of  percentage  of  C02,  reading 
from  zero  at  the  top  to  20%  at  the  bottom.  Each  chart,  corre- 
sponding to  one  complete  revolution  of  the  drum,  gives  a  record  for 
24  hours. 

The  actuating  stops,  Jl  and  /2,  shown  in  Fig.  137,  are  so  ad- 
justed that  the  motion  of  the  motor  is  reversed  the  moment  that 
the  pen  has  completed  its  upward  stroke.  The  sealing  liquid  then 
recedes  again,  the  potash  falls  back  to  its  original  level  mark  ra3, 
and  the  remaining  gas  mixture  is  drawn  out  of  vessels  N,  J1?  and 
J2,  and  passes  into  the  atmosphere. 

As  soon  as  the  level  of  the  sealing  liquid  has  fallen  below  the  gas 
inlet  from  tube  7,  a  constant  supply  of  fresh  gas  is  continually 
pumped  through  the  instrument,  until  the  returning  seal  again 
bottles  off  a  fresh  portion  for  analysis  in  the  same  manner  as  above 
described.  This  process  can  be  repeated  as  rapidly  as  desired,  the 
result  of  each  analysis  being  recorded  on  the  chart  by  a  vertical 
line.  The  tops  of  the  various  lines  form  a  continuous  curve,  show- 
ing the  percentage  of  CO,  in  the  flue  gases  at  any  time  during  the 
24  hours. 

A  facsimile  of  a  chart  made  by  this  apparatus  is  shown  in  Fig. 
140. 


FLUE  GAS  ANALYSIS 


279 


Application  of  the  Apparatus. — The  recorder  should  be  located 
in  the  fire-room  in  such  place  as  will  be  readily  accessible  but 
where  it  will  be  free  from  injury  while  working  the  fires.  The 
gases  to  be  analyzed  should  be  taken  from  the  uptake  on  the  boiler 
side  of  the  damper  and  conveyed  to  the  recorder  through  ordinary 
f-inch  gas  piping.  By  running  a  system  of  branch  pipes,  tapping 
the  uptake  of  each  boiler,  and  connecting  through  a  main  pipe  to 
the  recorder,  separate  readings  may  be  taken  for  all  of  the  boilers 
at  will.  A  cock  or  valve  should  in  such  case  be  fitted  on  each 
branch. 

^tTCo  a  record  Average  for  24  hrs     /<f-    %       Date     ssyz^/ef 

H"TC  in  n  x  i  BH~  DiniyY^^nYiDiixiLin  i~n  IBY- 


FIG.  140. 


Filter. — In  order  that  the  gases  may  be  free  from  impurities 
when  passing  through  the  apparatus,  a  filter  of  special  construction 
is  provided  with  each  outfit,  and  should  be  inserted  in  the  supply 
pipe  as  close  to  the  boiler  as  practicable. 

The  filter  is  filled  with  fine  wood  shavings,  intercepted  by  a  layer 
of  sawdust.  The  lid  is  provided  with  a  glycerine  seal.  At  the 
bottom  is  attached  a  water  separator  in  which  any  water  that  may 
condense  in  the  pipes  will  collect  and  may  be  drained  off  from  time 
to  time.  The  separator  is  filled  with  glycerine  to  a  given  mark  in 
order  to  exclude  the  air. 

Draught  for  Motive  Power. — This  is  obtained  from  the  base  of 
smoke  pipe,  above  damper,  and  is  brought  through  a  1-inch  pipe 
to  the  recorder,  where  the  connection  is  made  by  rubber  tubing. 
About  |-inch  draught  pressure  is  all  that  is  required  for  the  opera- 
tion of  the  apparatus. 

The  Uehling  C02  Recorder. — Eef erring  back  to  Fig.  26  if  a  con- 
stant vacuum  of  say  48  inches  of  water  be  maintained  in  chamber 
C"  and  the  two  apertures  A  and  B  are  of  the  same  size  and  are 


280  EXPERIMENTAL  ENGINEERING 

maintained  at  the  same  temperature,  the  manometer  p  will  show 
about  one  half  the  vacuum  maintained  in  Cf  due  to  the  fact  that 
the  apertures  oppose  equal  resistance  to  the  passage  of  the  gas. 

This  relation  will  be  maintained  so  long  as  the  same  volume  of 
gas  flows  through  B  as  enters  at  A.  If,  however,  a  constituent  of 
the  gas  (C02)  be  continuously  taken  away  or  absorbed  in  passing 
through  chamber  C  the  vacuum  therein  will  be  correspondingly  in- 
creased. This  increase  of  vacuum  in  C,  shown  by  the  manometer  p, 
therefore  correctly,  indicates  the  volume  of  the  gas  to  be  deter- 
mined. 

In  the  complete  instrument  the  suction  is  produced  by  a  steam 
aspirator  and  is  automatically  regulated  to  48  inches  of  water. 
Both  apertures  are  kept  at  a  constant  temperature  by  the  exhaust 
steam  from  the  aspirator  and  are  protected  by  efficient  niters. 
The  C02  is  absorbed  between  the  two  apertures  of  a  dilute  solu- 
tion of  caustic  soda  and  the  space  between  these  apertures  is  con- 
nected with  a  manometer  which  is  provided  with  a  scale  calibrated 
in  per  cent  of  C02.  This  manometer  may  be  placed  on  or  near 
the  boiler  front  showing  continuously  the  percentage  of  C02  for 
the  information  of  the  fire  room  force,  or  there  may  be  a  recording 
gage  similar  to  those  shown  in  Chapter  III,  adjusted  to  give  a 
continuous  record. 

TIME  FIRING  DEVICES. 

The  object  of  these  devices  is  to  automatically  give  audible  and 
visual  signals  in  each  fire  room  at  regular  time  intervals.  The 
audible  signal  calls  attention  to  the  visual  signal,  which  indicates 
the  furnace  that  is  to  be  fired.  The  time  intervals  can  be  varied  at 
will  from  20  seconds  to  9  minutes,  thus  ensuring  regular  firing 
and  working  of  the  fires  at  all  speeds  from  the  lowest  to  the 
highest. 

Each  ship  is  provided  with  a  transmitter,  located  in  the  work- 
ing engine  room,  and  an  indicator  in  each  fire  room.  Fig.  141 
shows,  in  elementary  form,  a  typical  arrangement  for  a  battleship. 
The  transmitter  contains  the  timer  and  suitable  mechanism  for  set- 
ting it  for  the  desired  time  intervals,  the  mechanism  for  closing 
the  indicator  circuits  at  these  time  intervals,  and  cut  out  switches 
and  fuses,  so  that  any  indicator  may  be  readily  cut  out  of  circuit 


TIME  FIRING  DEVICES 


when  desired.  The  indicators  are  constructed  to  suit  the  number 
of  furnaces  in  the  fire  rooms  in  which  they  are  installed.  The 
devices  are  connected  to  the  ship's  lighting  circuits,  operating  at 
125  volts  on  later  vessels  and  80  volts  on  those  of  earlier  date. 

These  principles  govern  the  design  of  all  devices  of  this  kind 
that  have  been  introduced  in  the  service. 

A  comparison  of  the  different  devices  is  afforded  by  a  brief 
description  of  the  mechanism  for  controlling  the  time  interval  in 
transmitters,  the  method  of  operation  of  indicators,  and  an  ele- 
mentary wiring  diagram  of  each  type. 


FIG.  141. 

The  Corey  Time  Firing  Device.  Old  Type. — This  has  been  sup- 
plied to  a  number  of  our  ships.  A  diagram  is  shown  in  Fig.  142, 
from  which  the  operation  will  be  understood.  A  small  constant- 
speed  motor  is  geared  to  the  wheel  A  and  this,  through  the  small 
friction  wheel  B,  operates  wheel  C.  A  and  C  are  flat  discs,  while 
B  is  carried  in  a  frame  by  the  screw  shaft  D,  and  its  position  is 
adjusted  by  the  thumb  screw  E.  By  changing  the  position  of  B 
we  change  the  relative  speed  of  A  and  C.  An  index  is  provided  to 
indicate  the  firing  interval,  as  regulated  through  B  by  the  speed  of 
revolution  of  C. 

Two  contactors,  F  and  G,  are  seen,  which  are  closed  and  opened 
alternately  six  times  for  each  revolution  of  C.  These  make  con- 
nections to  the  coils  of  a  pair  of  electromagnets,  shown  near  the 
bottom  of  the  diagram.  These  in  turn  make  and  break  the  cir- 
cuits for  operating  the  starboard  and  port  indicators  respectively, 
in  the  fire  rooms. 


2S2 


EXPERIMENTAL  ENGINEERING 


The  receiver  consists  essentially  of  an  electromagnet,  the  arma- 
ture of  which  carries  an  escapement  that  operates  a  shaft,  and  this 
in  turn  carries  a  dial  with  the  signal  numbers  on  it.  It  will  be 


noted  that  there  are  twelve  displays  for  a  complete  revolution  of 
the  shaft,  the  numbers  from  1  to  6  being  repeated.  This  gives  a 
better  arrangement  of  the  mechanism. 


TIME  FIRING  DEVICES 


283 


Three  wires  only  are  necesary  in  the  conduits  leading  to  each 
fire  room.  One  of  these  is  to  the  electromagnet,  one  to  the  lamp, 
and  the  third  is  a  common  return. 


E 


E 


FIG.  143. 


FIG.  144. 


Corey  Time  Firing  Device.  New  Type. — Figs.  143  and  144  show 
external  views  and  the  wiring  diagram  respectively  of  the  trans- 
mitter and  indicator.  The  transmitter  contains  a  shunt-wound 


284  EXPERIMENTAL  ENGINEERING 

motor,  A,  running  at  a  constant  speed  of  1600  revolutions  per 
minute.  Through  suitable  worm  gears  for  reducing  the  speed, 
this  motor  drives  a  gear  wheel  R,  at  a  speed  of  one-fifth  of  a  revo- 
lution per  minute.  An  arm  D,  carrying  an  insulated  pin  E  at  its 
end,  is  rigidly  secured  to  this  gear  wheel.  On  the  shaft  C  is  an 
ami,  carrying  contact  springs  H,  which  can  be  set  at  any  desired 
angle  by  means  of  a  pointer  and  handle  (V,  Fig.  143),  located 
on  the  front  of  the  transmitter  case,  and  secured  to  the  shaft  C. 
Current  is  supplied  to  these  contact  springs  through  collector  rings 
and  brushes  F  and  G. 

There  are  two  electromagnetic  relays  L  and  M ,  which  are  alter- 
nately energized  when  the  pin  E,  carried  by  the  revolving  arm  D , 
makes  contact  between,  first  the  movable  contact  springs  H,  and 
afterwards  the  fixed  contact  springs  K.  This  causes  the  rocker 
armature  N  to  alternately  close  the  two  sets  of  knife-blade  switches 
0  and  P,  reversing  the  direction  of  rotation  of  the  motor,  and 
therefore  of  the  arm  D.  These  sets  of  switches  0  and  P  also  trans- 
mit indications  alternately  to  the  starboard  and  port  indicators. 

Since  the  speed  of  revolution  of  the  arm  D,  carrying  pin  E,  is 
constant,  the  desired  time  intervals  are  obtained  by  varying  the 
angle  between  the  fixed  contact  springs  K  and  the  movable  springs 
H. 

Two  lamps,  R  and  S,  are  provided  in  the  transmitter,  one  show- 
ing through  a  green  glass  when  signals  are  sent  to  starboard  fire 
rooms  and  the  other  through  a  red  glass  when  the  port  indicators 
are  operated. 

Fused  cut-out  switches  T  are  installed  in  the  bottom  of  the  trans- 
mitter case. 

The  indicators  with  this  device  are  similar  to  those  used  with 
the  earlier  type  of  Corey  device,  except  that  each  indicator  requires 
only  two  wires. 

Kilroy  Time  Firing  Device. — Figs.  145  and  146  show  the  ex- 
ternal appearance  and  wiring  diagram,  respectively,  of  the  trans- 
mitter and  indicator  of  this  device. 

The  transmitter  contains  three  electromagnets,  A,  B  and  C,  two 
of  which,  B  and  Cf  are  so  arranged  that  they  will  alternately  attract 
a  pivoted  armature  D,  which  operates  an  automatic  switch  G,  thus 


TIME  FIRING  DEVICES 


285 


closing  the  current  alternately  through  the  winding  of  the  magnets. 
A  condenser  c  is  connected  across  the  line  to  reduce  the  spark. 
The  armature  D  is  geared  to  a  thin  copper  disc  (not  shown)  which 


r      REGULATOR       ^1 

I  FOd  KIUROY'S  PATENT 
I  STOKING  INDICATORS 
I                NO.  1=3 
I  EVEKHEDSVIOiOl.ES'-'"'  | 
t^        LONDON. ^> 


o«7 


6 


¥ 


FIG.  145. 


FIG.  146. 


revolves  in  the  field  of  the  upper  electromagnet  A  and  serves  as  a 
brake  or  retarder  for  the  armature  D.  The  different  time  intervals 
are  controlled  by  regulating  the  strength  of  the  field  of  magnet  A. 
This  is  done  by  means  of  the  rheostat  R,  the  regulation  of  which 


286  EXPERIMENTAL  ENGINEERING 

is  effected  by  means  of  the  pointer  V,  located  on  the  front  cover 
of  the  transmitter.  There  is  a  dial  with  suitable  lettering  for 
setting  the  pointer  for  the  desired  time  interval. 

The  magnet  A  is  wired  in  parallel  with  magnets  B  and  C,  so  that 
the  strength  of  the  field  of  magnet  A,  in  which  the  copper  brake 
disc  revolves,  and  the  pull  of  magnets  B  and  C  on  armature  D  may 
keep  the  same  relation  to  each  other.  By  this  arrangement  the 
accuracy  of  the  time  intervals  will  not  be  affected  by  changes  in 
strength  of  the  supply  current. 

On  one  side  of  the  transmitter  are  located  fuse  blocks  F  and  cut- 
out switches  S,  through  which  current  is  supplied  to  the  several  in- 
dicators. It  will  be  noted  that  the  automatic  switch  G  is  so 
arranged  that  it  permits  current  to  pass  through  only  half  the 
indicators  at  one  time.  Usually  signals  are  sent  alternately  to  the 
starboard  and  port  fire  rooms. 

Each  indicator  contains  an  electromagnet  M ,  with  two  armatures, 
N  and  0,  one  of  which  strikes  a  gong  P,  and  the  other  revolves  a 
disc  U,  by  means  of  a  ratchet  and  pawl  mechanism  L.  The  dial  U 
has  numerals  spaced  at  regular  intervals  around  its  outer  edge, 
which  become  visible  when  opposite  the  opening  T  in  the  front 
cover  of  the  indicator. 

Sub-Target  Gun  Company's  Time  Firing  Device. — Figs.  147  and 
148  show  the  external  appearance  and  wiring  diagram,  respectively, 
of  the  transmitter  and  indicator  for  this  device. 

The  timer,  A,  consists  of  an  electromagnet  of  special  construc- 
tion, with  an  oscillating  armature  (not  shown)  which  serves  to 
alternately  open  and  close  the  current  through  the  magnet  coils. 
A  spring  attached  to  this  armature  pulls  it  away  from  the  magnet 
poles  when  the  circuit  is  open.  A  small  fan  is  geared  to  the  arma- 
ture and  spring,  the  motion  of  which  is  retarded  by  the  air  resist- 
ance, causing  it  to  act  as  a  brake  to  regulate  the  time  required  for 
the  armature  to  make  one  complete  oscillation  or  beat.  The  device 
is  adjusted  so  that  this  time  is  three  seconds. 

At  each  beat  of  the  armature,  the  switch  B  is  first  closed,  then 
opened,  energizing  a  second  magnet  C.  This  transmits  current  to 
one  of  the  magnets  D  or  E,  geared  to  a  spindle  F,  so  as  to  cause  it 
to  revolve  alternately  in  opposite  directions.  A  contactor  block  G 


TIME  FIRING  DEVICES 


287 


is  threaded  on  this  spindle,  so  that  it  will  travel  back  and  forth 
between  a  pair  of  fixed  contact  springs  H  and  a  pair  of  adjustable 
contact  springs  I.  When  the  spindle  is  being  driven  by  one  of  the 


I 


O 


FIG.  147. 


FIG.  148. 


electromagnets,,  D  for  example,  the  contactor  will  move  toward  the 
fixed  contact  H  a  certain  distance  each  time  the  magnet  D  is  ener- 
gized, i.  e.,  every  three  seconds.  When  contact  is  made  at  H  the 
magnet  C  is  energized,  thus  reversing  the  switch  K,  throwing  mag- 


288  EXPERIMENTAL  ENGINEERING 

net  D  out  and  magnet  E  in  circuit.  This  causes  the  contactor  Q 
to  move  at  regular  intervals  in  the  other  direction  until  contact  is 
made  at  I,  when  magnet  E  is  cut  out  of  circuit  and  D  thrown  in 
again. 

Since  the  contactor  0  moves  an  equal  distance  every  three 
seconds,  it  is  noted  that  the  desired  time  intervals  may  be  ob- 
tained by  regulating  the  distance  between  contacts  H  and  I.  This 
is  done  by  means  of  a  small  hand  wheel  M  (Fig.  147)  on  the  front 
cover  of  the  transmitter,  which  is  geared  to  the  movable  block 
holding  the  contact  springs  I.  A  dial  and  pointer  N,  on  the  front 
of  the  transmitter,  shows  the  time  interval  at  which  it  is  set.  A 
lamp  L  shows  through  an  opening  0  in  the  front  of  the  transmitter 
each  time  signals  are  sent  to  the  fire  rooms. 

The  magnet  C,  in  addition  to  directing  current  to  magnets  D 
and  E,  also  operates  switch  P,  closing  the  circuit  through  the  indi- 
cators each  time  contact  is  made  at  H  or  I. 

The  indicator  contains  a  magnet  Q,  the  armature  of  which  re- 
volves a  dial  R  through  a  ratchet  and  pawl  mechanism,  not  shown. 
The  dial  carries  the  perforated  numerals  1,  2,  3,  etc.,  denoting  the 
furnaces  in  the  fire  rooms.  The  magnet  Q  also  lights  the  lamps  T, 
located  behind  the  dial  R  and  illuminates  the  numerals ;  also  closes 
the  circuit  through  a  magnet  U  and  sounds  a  gong  V  each  time  a 
signal  is  received. 

General  Electric  Company's  Time  Firing  Device.  New  Type. — 
The  principle  parts  of  the  transmitter  in  this  device  are  shown 
diagrammatically  in  Fig.  149. 

A  shunt- wound  motor,  A,  runs  at  a  constant  speed  and  drives, 
through  suitable  reducing  gears,  a  cam  shaft,  B,  at  a  speed  of  2 
revolutions  per  minute.  This  shaft  carries  a  cam  C,  which  rotates 
a  ratchet  wheel  E,  by  means  of  a  lever  D  and  pawl  F.  Another 
pawl,  N}  holds  the  ratchet  wheel  when  pawl  F  is  being  lifted. 

The  ratchet  wheel  E  carries  a  pin  H  which,  at  a  certain  position 
of  its  revolution,  strikes  the  arm  of  a  retaining  pawl  I  and  disen- 
gages it,  releasing  a  rock  shaft  K  and  throwing  contact  arm  L 
against  cam  M,  thus  closing  the  circuit  to  the  indicators.  At  the 
same  time  arm  P  strikes  arm  Q  and  disengages  pawls  F  and  N. 
Eatchet  wheel  E  is  then  drawn  back  by  spring  Q  until  pin  H 
brings  up  against  an  adjustable  stop  R. 


TIME  FIRING  DEVICES 


289 


Just  before  cam  C  again  begins  to  raise  the  lever  D,  the  con- 
tact arm  L  snaps  off  cam  M,  breaking  the  circuit  to  the  indicators. 
Then,  as  the  lever  D  is  lifted,  the  arm  Q  raises  rocker  arm  P,  thus 
resetting  the  other  end  of  same  under  the  retaining  pawl  I.  This 
holds  the  contact  arm  L  clear  of  cam  M  until  pin  II  again  strikes 
pawl  I. 

It  will  thus  be  seen  that  since  cam  shaft  B  revolves  at  a  constant 


FIG.  149. 

speed  of  2  revolutions  per  minute,  the  ratchet  wheel  E  will  be  re- 
volved through  an  equal  angle  every  thirty  seconds,  and  the  desired 
time  intervals  are  obtained  by  regulating  the  angular  distance  be- 
tween retaining  pawl  I  and  adjustable  stop  R.  This  is  done  by 
means  of  a  dial  and  pointer  T  located  on  the  outside  of  the  trans- 
mitter case. 

It  will  be  noted  that  the  movement  of  rock  shaft  K  causes  a 
pawl  V  to  rotate  a  ratchet  wheel  W,  which  carries  a  number  signal 

J-  y  o 

cylinder  0.     This  cylinder  supports  a  number  of  contact  blocks 
19 


290 


EXPERIMENTAL  ENGINEERING 


which,  by  making  contact  with  the  several  springs  Y,  cause  to  be 
indicated  the  number  of  the  furnace  to  be  fired.  A  slotted  wheel 
X  with  roller  and  arm  serves  to  hold  the  cylinder  in  position.  It 
will  be  noted  that  the  movement  of  the  cylinder  always  occurs 
when  the  circuit  is  open,  so  that  the  circuit  is  made  and  broken 
only  by  the  arm  L  on  cam  M . 


FIG.  150. 


FIG.  151. 


Switches  and  fuses  are  located  in  the  base  of  the  transmitter. 

The  Indicator. — This  consists  of  a  number  of  5-candle-power 
lamps  and  an  electromagnet  in  a  water-tight  case.  A  glass-covered 
opening  in  front  of  each  lamp  is  covered  by  a  piece  of  metal  having 
a  number  cut  in  silhouette,  so  that  each  lamp,  when  lighted,  will 
indicate  the  number  of  a  furnace  to  be  fired.  The  electromagnet 
operates  a  gong  located  on  the  outside  of  the  case,  and  attracts 
attention  to  each  change  of  signal. 


TIME  FIRING  DEVICES  291 

This  device  has  the  advantage  of  eliminating  all  coils,  with  few 
make  and  break  contacts  in  the  transmitter,  and  also  the  elimina- 
tion of  moving  parts  in  the  indicator.  The  disadvantages  are  the 
large  number  of  working  mechanical  parts  in  the  transmitter,  and 
if  there  should  be  a  failure  of  any  of  the  lamps  of  the  indicator 
there  would  be  a  corresponding  failure  in  the  display  of  the  num- 
ber corresponding  to  such  lamp. 

An  elementary  wiring  diagram  of  a  transmitter  and  an  indicator 
are  shown  in  Fig.  150.  Outside  views  of  these  parts  are  shown  in 
Fig.  151. 

The  Lobitz  Time  Firing  Device. — This  device  was  designed  by 
Machinist  Henry  Lobitz,  U.  S.  N".,  and  the  initial  installation  was 
made  and  installed  by  the  ship's  force  on  board  the  U.  S.  S. 
Minnesota. 

Eef erring  to  Fig.  152,  there  is  a  small  leather-bound  friction 
wheel,  2-|  inches  diameter,  placed  on  a  shaft  driven  from  the  main- 
engine  revolution-indicator  gear.  The  wheel  is  driven  through 
worm  gearing  proportioned  to  give  one  revolution  of  the  wheel  for 
two  hundred  revolutions  of  the  main  engine. 

The  friction  wheel  makes  contact  with  the  face  of  and  drives 
an  18-inch  disc  as  shown.  The  friction  wheel  is  loosely  mounted 
on  its  shaft,  with  a  sliding  feather  for  driving  it  and  with  an  ad- 
justing screw  for  varying  its  distance  from  the  center  of  the  disc. 
The  pressure  between  the  face  of  disc  and  circumference  of  fric- 
tion wheel  can  be  varied  by  an  adjusting  nut  at  the  center  of  the 
disc.  This  nut  has  a  ball-bearing  under  it  to  lessen  friction. 

Gong  Signals. — The  circumference  of  the  disc  carries  four  lugs 
spaced  90°  apart.  These  lugs  carry  one,  two,  three  and  four  teeth, 
respectively.  As  the  disc  revolves,  each  tooth  in  turn  engages  the 
contact  maker,  shown  at  the  right  in  the  figure,  and  closes  a  circuit 
leading  to  an  electric  gong  in  each  fire  room.  The  gongs  are  thus 
made  to  strike  one,  two,  three  and  four  times  at  regular  intervals, 
the  length  of  the  intervals  depending  upon,  first,  the  speed  of  the 
main  engines,  and,  second,  on  the  distance  of  the  friction  wheel 
from  the  center  of  the  disc. 

The  index  plate  at  the  right  indicates  the  proper  setting  of  the 
friction  wheel  for  any  firing  interval  that  may  be  desired. 


292 


EXPERIMENTAL  ENGINEERING 


TIME  FIRING  DEVICES  293 

Visual  Signals. — On  the  shaft  of  the  rotating  disc  there  is  a  6- 
inch  hard-rubber  disc  with,  first,  a  copper  ring,  and,  second,  four 
segments  of  a  copper  ring  at  equal  intervals  around  its  circum- 
ference. 

On  the  friction  disc  there  is  a  carbon  holder  which  rides  over 
the  copper  ring  and  the  segment.  Each  segment  is  wired  to  a  lamp 
in  a  light  box  placed  in  each  fire  room,  the  light  box  having  the 
figures  1,  2,  3,  4  on  it.  When  the  gong  strikes  one,  the  figure  one 
is  lighted  up  in  the  light  box — 2  gongs :  No.  2,  lights  up ;  and  so  on. 


QUESTIONS  ON  THE  TEXT. 

CHAPTER  I. 

1.  What  is  experimental  engineering?    What  tests  are  made  in  con- 
nection with  marine  engineering  work  and  for  what  purposes?     Why 
are  numerous  tests  made  of  different  samples  from  the  same  lot  of 
material?    Does  this  lead  to  more  accurate  results,  and  if  so,  why? 

2.  Explain  the  value  of  accuracy  in  engineering  calculations  and  the 
necessity  for  discrimination  in  the  effort  to  obtain  accurate  results. 

3.  What  are  direct  and  indirect  measurements?   Give  examples.   What 
determines  the  degree  of  accuracy  for  which  a  quantity  is  measured? 
Explain  the  limits  of  error  in  observations. 

4.  Explain  the  use  of  a  series  of  observations  in  determining  the  most 
probable  value:     (1)  Where  the  observations  have  been  made  with  care, 
(2)  where  they  are  not  all  equally  reliable. 

5.  Discuss  sources  of  error,  the  different  classes  of  errors  and  how  to 
avoid  them.    Distinguish  between  mistakes  and  errors  of  observation. 

6.  Explain  the  term  significant  figures  and  how  to   determine  the 
degree  of  accuracy  of  the  various  places  of  significant  figures  in  an 
observed  quantity  when  its  average  deviation  is  known. 

7.  Give  the  rules  for  significant  figures  and  illustrate  by  examples. 

8.  What  procedure  should  be  followed  in  computing  the  results  of  a 
test?    What  details  should  be  included  in  the  report? 

CHAPTER  II. 

9.  What  is  a  logarithmic  scale,  how  constructed  and  what  do  the 
figures  on  it  represent?    Explain  the  use  of  the  logarithmic  scale:  (1) 
in  multiplication,   (2)   in  division.     If  the  pointer  should  fall  off  the 
scale  what  is  done? 

10.  Explain  the  construction  of  Sexton's  omnimetre.    How  determine 
the  logarithm  of  a  number  by  the  use  of  this  instrument? 

11.  Briefly  describe  the  functions  of  the  several  circles  of  the  omni- 
metre and  explain  in  detail  how  you  would  proceed  to  find  the  value  of 
a  formula  expressed  in  the  form: 

a  x  sin  ft  x  C*  X  sec  &  X  & 
f  x  tan  ff  x  vers  sinTi 

12.  Explain  the  use  of  the  omnimeter  in  solving  problems  of  the  form 
x  =  Vaa-|-  ft2  and  #—  Vo2  —  b2. 

13.  Explain  the  construction  of  Fuller's  calculating  instrument  and  of 
Sperry's  Pocket  Calculator.    For  what  classes  of  work  are  each  of  these 
adapted? 

14.  Explain  the  use  of  the  straight  slide  rule.    How  does  it  differ  from 
the  single  logarithmic  scale  and  what  is  the  advantage  gained  thereby? 

15.  Explain   the   construction    of   Thacher's    calculating    instrument. 
What  is  the  essential  difference  between  this  and  the  Fuller  instrument 
and  wherein  lie  the  advantages  of  each? 


QUESTIONS  ON  THE  TEXT  295 

16.  Explain  the  construction  and  use  of  the  duplex  slide  rule. 

17.  Make  a  line  sketch  of  the  Amsler  polar  planimeter.     Letter  and 
name  the  essential  parts.     What  is  the  zero  circle?     How  is  its  value 
obtained  and  how  is  it  applied?    What  feature  makes  this  instrument 
adaptable  for  use  in  computing  indicator  ends? 

18.  Demonstrate  the  accuracy  of  the  Amsler  polar  planimeter  in  meas- 
uring areas  outside  the  zero  circle  and  show  that  the  demonstration  is 
general. 

19.  Make  a  plan  view  of  Coffin's  averaging  instrument,  showing  an 
indicator  card  in  position;  explain  how  to  adjust  the  card  and  the  in- 
strument prior  to  measuring  the  card  and  describe  the  method  employed 
in  measuring  (1)  the  area  of  the  card,  (2)  its  mean  ordinate. 

20.  Demonstrate  the  theory  of  the  Coffin  averaging  instrument  and 
show  how  the  instrument  is  a  special  form  of  the  Amsler  planimeter. 

CHAPTER  III. 

21.  Sketch  the  Pratt  and  Whitney  measuring  machine.     Letter  and 
name  its  essential  parts.    Describe  in  detail  the  method  of  adjusting  the 
machine  to  zero  and  measuring  an  object  in  the  machine. 

22.  Show  by  line  sketches  the  detail  construction  of  a  Bourdon  gage 
and  a  diaphragm  gage. 

23.  Distinguish,  illustrating  by  sketches,  between  single  and  double 
tube  Bourdon  gages.     Which  is  preferred  and  why? 

24.  How  are  the  dials  of  pressure  and  vacuum  gages  graduated?  What 
is  a  compound  gage  and  how  is  it  graduated? 

25.  Sketch  and  explain  the  essential  features  of  a  recording  pressure 
gage.     Show  by  an  additional  sketch  the  recording  mechanism  of  an 
air  pressure  gage. 

26.  Show  by  sketch  the  working  principle  of  the  Uehling  differential 
recorder.    Letter  the  different  parts  and  explain  its  operation. 

27.  Make  a  line  sketch,  showing  the  essential  features  of  a  standard 
steam  and  vacuum  gage  testing  apparatus.     Explain  in  detail  how  to 
conduct  a  test  with  this  outfit. 

28.  How  are  gages  tested  on  board  ship?    What  is  a  manometer  and 
for  what  purpose  is  it  used?     How  are  manometer  readings  expressed? 

29.  What  is  the  practical  high  temperature  limit  of  an  ordinary  mer- 
curial thermometer  and  why?     What  are  the  different  types  of  pyrom- 
eters? 

30.  Explain    the    principle    on   which    the   gas   thermometer    is    con- 
structed.   Make  line  sketch,  showing  the  construction  of  the  Industrial 
Thermograph.    Explain  its  action  and  state  the  material  used  in  filling 
the  bulbs  for  various  ranges  of  temperature. 

31.  Make  diagrammatic  sketch  and  explain  the  underlying  principle 
in  Uehling's  pneumatic  pyrometer. 

31.  Make  diagrammatic  sketch  of  all  the  parts  in  Uehling's  pneumatic 
pyrometer  and  explain  its  operation. 

32.  Make  line  sketch   of  Uehling's  pneumatic  pyrometer   assembled 
complete.    Also  sectional  view  of  the  bulb.    Explain  how  the  instrument 


296  EXPERIMENTAL  ENGINEERING 


is  connected  up  for  use  and  how  it  may  be  used  for  a  whole  battery  of 
boilers. 

33.  How  does  a  mercurial  pyrometer  differ  from  a  mercurial  ther- 
mometer and  why?    What  are  the  advantages  of  and  limitations  on  such 
an  instrument?     Explain  the  construction  of  an  expansion  pyrometer. 
What  are  its  advantages  and  disadvantages? 

34.  Explain  the  calorimetric  pyrometer.     Write  and  explain  the  for- 
mula on  which  it  is  based.     What  are  its  limitations?     Explain  the 
thermo-electric  pyrometer.     What  materials  are  used  in  making  up  the 
elements  for  different  ranges  of  temperature? 

35.  Make  line  sketch,  showing  the  wiring  arrangement  in  the  resist- 
ance pyrometer.    Explain  its  principle  of  operation. 

36.  Show  by  line  sketch  the   principle  of  the  reflecting  pyrometer. 
What  is  the  rule  for  its  working  distance  from  the  hot  body? 

37.  Sketch  an  engine  counter.    What  are  maneuvering  indicators  and 
how  fitted?    Explain  a  differential  counter  gear  for  multiple  shafts. 

38.  Make  line  sketch  and  explain  the  operation  of  a  tachometer  for 
high  speed  engines. 

39.  Make  line  sketches  and  explain  the  transmitter  and  receiver  in  a 
Hutchison  marine  tachometer. 

40.  Explain  the  principle  of  the  Hopkins  electric  tachometer.     What 
fault  is  possessed  by  electric  tachometers  in  general  and  how  is  it  over- 
come?   Explain  the  McNab  marine  register  and  indicator. 

41.  Sketch  and  explain  the  operation  of  the  Davison  speed  regulator. 

42.  What  is  the  Taylor  counter?    The  Bailey  counter?    Explain  with 
line  sketch  the  precision  tacograph  and  its  use. 

CHAPTER  IV. 

43.  Define  or  explain  the  following  thermodynamic  terms:      (1)   heat, 
(2)   quantity  of  heat,  (3)   temperature,  (4)   absolute  temperature,   (5) 
entropy,   (6)    boiling  point,   (7)   British  thermal  unit   (B.   T.   V.},   (8) 
specific  Ueat,  (9)  sensible  heat,  (10)  latent  heat,  (11)  total  heat,  (12) 
Joule's  equivalent,  (13)  saturated  steam,  (14)  wet  steam,  (15)  super- 
heated steam,  (16)  quality  of  steam. 

44.  What  are  the  three  general  classes  of  steam  calorimeters?     Give 
an  example  of  each  class,  and  briefly  state  the  principle  of  construction 
and  operation. 

45.  Sketch  and  explain  Carpenter's  throttling  calorimeter,   deriving 
the  general  equation  for  its  use.     Explain  with  diagram  the  graphical 
solution. 

46.  Explain  the  calibration  method  for  the  use  of  Carpenter's  throt- 
tling calorimeter  and  derive  the  equation.     Discuss  briefly  the  limita- 
tions of  the  instrument. 

47.  Sketch  Thomas'  superheating  steam  calorimeter  and  connections. 
Briefly  describe  its  operation  and  derive  equations  for  its  use. 

48.  Sketch  Carpenter's  separating  steam  calorimeter  and  connections 
and  derive  the  equations  used  with  it. 

49.  Derive  equations  for  use  in  connection  with  the  barrel  calorimeter. 
Describe  the  test,  stating  precautions.     In  all  calorimeter  experiments 
what  care  must  be  exercised  in  sampling  the  steam? 


QUESTIONS  ON  THE  TEXT  297 

50.  Discuss  the  temperature-entropy  diagram  for  water,  and  show  its 
application  to  steam.     Explain  the  difference  between  isothermal  and 
adiabatic  lines  on  the  diagram. 

51.  Discuss  the  temperature-entropy  diagram  (1)  for  an  ideal  engine, 
(2)  for  a  real  engine. 

CHAPTER  V. 

52.  For  what  purposes  are  water  meters  employed  by  naval  engineers? 
Describe  the  Worthington  water  meter.    How  is  the  rate  of  flow  deter- 
mined?   What  are  the  disadvantages  attending  the  use  of  water  meters, 
as  usually  constructed,  on  board  ship? 

63.  Sketch  and  describe  the  Keystone  water  meter. 

54.  Make  sketch   in   section   of  the  Venturi   meter  and   describe   its 
operation.    Make  line  sketch  of  the  recording  apparatus. 

55.  Derive  equations  for  use  with  the  Venturi  meter. 

56.  Explain  with  sketches  the  early  forms  of  Pitot's  tube  used  for 
measuring  the  rate  of  flow  of  water. 

57.  Sketch  and  explain  the  operation  of  Darcy's  improved  form  of 
Pitot's  tube  for  measuring  the  rate  of  flow  of  streams. 

58.  In  the  pitometer,   sketch  the  street  connection,   rod  meter  and 
manometer   in   place.     Explain   how   this    instrument  is   inserted   and 
adjusted  for  use  in  a  water  main. 

59.  Sketch  the  street  connection  for  use  with  a  pitometer  and  explain 
the  traverse. 

60.  What  is  a  weir?     Give  general  features  of  construction,  stating 
the  points  that  must  be  observed  in  order  to  obtain  accurate  results. 

61.  Describe  the  construction  and  operation  of  a  tank  for  weir  ap- 
paratus, illustrating  with  free-hand  sketches. 

62.  Describe  the  construction,  operation  and  use  of  the  hook  gage. 
Explain  with  sketch   the  triangular  notched   weir  and  write  the  for- 
mulas for  its  use.     What  are  its  advantages?     Explain  what  is  meant 
by  miner's  inch. 

CHAPTER  VI. 

63.  Sketch  an  anemometer  and  explain  how  it  should  be  used.     To 
what  extent  may  its  indications  be  relied  upon? 

64.  Sketch  the  special  form  of  Pitot's  tube  used  in  Taylor's  method 
of  measuring  low  air  velocities.     How  is  this  used  to  obtain  the  mean 
velocity  in  a  pipe  of  circular  section? 

65.  Make  line  sketch  of  the  manometer  used  in  measuring  low  air 
velocities  by  Taylor's  method  and  explain  its  use. 

66.  Knowing  the  difference  between  impact  and  static  pressures  by 
Pitot's  tube  in  an  air  pipe,  how  proceed  to  calculate  the  rate  of  flow? 
How  may  a  single  Pitot  tube  be  used  in  tests  of  this  character? 

67.  Give  Napier's  rule  for  the  rate  of  discharge  of  steam  through  a 
nozzle.     What  are  its  limitations?     What  is  the  direct  measure  of  the 
efficiency  of  a  steam  engine?     How  is  this  usually  obtained  in  engine 
tests?    What  are  steam  meters  and  of  what  value  are  they? 

68.  Into  what  two  classes  are  steam  meters  divided?    Sketch  the  pipe 
connections  for  the  Sarco  steam  meter  in  horizontal  and  vertical  pipes, 


298  EXPERIMENTAL  ENGINEERING 

write  the  formula  for  the  flow  of  steam  under  these  conditions  and 
explain  its  operation. 

69.  Make  line  sketch  of  the  recording  mechanism  in  a  Sarco  steam 
meter  and  explain  its  operation. 

70.  Distinguish  between  shunt  and  series  steam  meters.     Sketch  the 
nozzle  plug  used  in  the  General  Electric  Company's  steam  flow  meter 
and  explain  its  use. 

71.  Explain  with  line  sketch  the  General  Electric  Company's  recording 
flow  meter  with  automatic  pressure  correction  device. 

72.  Explain  with  line  sketch  the  General  Electric  Company's   indi- 
cating flow  meter.    How  does  the  air  flow  meter  differ  from  the  steam 
flow  meter? 

CHAPTER  VII. 

73.  Explain  what  is  meant  by  (1)  power,  (2)  Horse  power,  (3)  indi- 
cated horse  power,  (4)  brake  Horse  power,  (5)  shaft  horse  power,  (6) 
metric  horse  power,  (7)  efficiency  of  a  machine.    What  is  the  relation 
between  indicated  horse  power  and  shaft  horse  power  in  an  ordinary 
steam  engine,  and  in  a  steam  turbine? 

74.  To  what  errors  is  the  steam  engine  indicator  subject  and  how  are 
they  corrected? 

75.  What  is  the  object  of  calibrating  indicator  springs?     What  pre- 
cautions should  be  observed?    Make  line  sketch  of  Carpenter's  indicator 
and  gage  tester  and  briefly  describe  its  operation. 

76.  Make  a  free-hand   line   sketch,   showing  the   essential   parts   of 
Cooley's  indicator  testing  apparatus,  and  give  a  brief  description  of  the 
apparatus. 

77.  Describe  fully  the  method  used  for  calibrating  an  indicator  spring, 
using  Cooley's  tester.     Illustrate  with  free-hand  sketch.     Explain  how 
the  results  are  calculated.    How  are  pressure  tests  below  the  atmosphere 
made? 

78.  Sketch   and  explain  the   operation  of  the  Hospitalier-Carpentier 
monograph.    For  what  class  of  engines  is  it  more  particularly  adapted? 

79.  Make  a  free-hand  sketch,  in  section,  of  Ripper's  mean  pressure 
indicator,  and  explain  the  operation  of  the  apparatus. 

80.  Make  a  line  sketch  of  Ripper's  power  board  and  show  the  infor- 
mation that  may  be  obtained  from  it.    Explain  its  construction,  show- 
ing that  it  is  merely  a  special  application  of  the  slide  rule.    From  the 
same  sketch  explain  Hudson's  power  scale. 

81.  Explain  in   detail  how  to  construct  a  logarithmic  diagram  for 
computing  horse  power. 

82.  Describe  with  sketch  the  Prony  brake,  explaining  its  use.     De- 
scribe the  water  brake.    How  may  a  dynamo  be  used  as  a  brake?    What 
is  electric  horse  power  and  how  is  it  made  use  of  to  determine  the 
indicated  horse  power?    What  is  a  belt  dynamometer? 

83.  Sketch  in  section  the  Kenerson  transmission  dynamometer  and 
explain  its  operation. 

84.  Make   line   sketch   showing  the  working   parts   of  the  Emerson 
power  scale  and  explain  its  operation. 


QUESTIONS  ON  THE  TEXT  299 

85.  Explain    the    principle    of    a    torsionmeter    for    measuring   horse 
power.    Draw  diagram  and  show  how  a  shaft  is  calibrated,  deducing  the 
equations. 

86.  Show  how  to  obtain  the  horse  power  with  a  torsionmeter  without 
calibration  of  shafting.    Why  is  it  necessary  to  calibrate? 

87.  Explain  the  operation  of  one  of  the  following  torsionmeters,  illus- 
trating   with    line    sketches:      Denny- Johnson,    Fottinger,    Hopkinson- 
Thring,  Metten.     What  are  the  advantages  and   disadvantages  of  the 
instrument  selected? 

88.  Discuss  briefly  torsionmeters  compared  with  the  indicator,  torsion 
readings  for  reciprocating  engines,  and  curves  of  chest  pressures  and 
horse  power. 

CHAPTER  VIII. 

89.  Define  or  explain  what  is  meant  by   (1)    stress,   (2)    strain,    (3) 
elasticity,   (4)   elastic  limit,   (5)  rigidity  or  stiffness,   (6)   coefficient  of 
ultimate  strength,    (7)    coefficient  of  strength  at  the  elastic  limit,   (8) 
percentage  of  elongation,   (9)   reduction  of  area  of  cross  section,   (10) 
modulus  of  elasticity,   (11)   modulus  of  resilience,   (12)    breaking  load, 
(13)  maximum  load,  (14)  safe  load,  (15)  factor  of  safety. 

90.  Make  a  line  sketch  of  a  stress-strain  diagram  and  explain  the  in- 
formation that  may  be  derived  from  it.    What  are  the  general  features 
of  construction  of  a  power  testing  machine? 

91.  Show  by  line  sketches  the  relative  positions  of  pulling  screws,  top 
and   pulling  heads,  weighing  table,   and   test   specimen,   in   using  the 
Riehle  screw  power  testing  machine    for  tests  as  follows:      (1)  tension, 
(2)  compression,  (3)  bending  and  shearing. 

92.  Make  a  line  sketch  showing  the  essential  features  of  a  Riehle 
screw  power  testing  machine.     Describe  briefly  the  automatic  apparatus 
for  keeping  the  scale  beam  in  balance.     Describe  the  autographic  ap- 
paratus.   For  what  purpose  is  an  extensometer  used?    What  is  the  yield 
point  f 

93.  Describe  the  behavior  of  the  two  general  classes  of  metals,  plastic 
and  brittle,  when  subjected  in  short  specimens  to  compressional  stress. 
What  information  may  be  obtained  in  each  case?    For  what  purpose  are 
cross  bending  tests  made? 

94.  Describe  the  practical  use  of  a  testing  machine.     What  informa- 
tion is  obtained?     What  is  placed  on  the  test  record?     Sketch  and  de- 
scribe the  standard  test  pieces  used  in  the  navy. 

95.  Describe  with  line  sketches  the  construction  and  operation  of  the 
Riehle-Miller  torsional  testing  machine.     Show  the  details  of  the  weigh- 
ing mechanism.    Explain  the  use  of  the  torsion  indicator. 

96.  Name  and  briefly  describe  the  different  varieties  of  cement.   What 
is  concrete?     Reenforced  concrete?     What  are  the  uses  of  cement  on 
board  ship? 

97.  Enumerate  and  briefly  describe  the  several  tests  to  which  cement 
is  subjected. 

98.  Sketch  a  cement  tensile  test  specimen  and  describe  how  these  are 
made. 

99.  Make  line  sketch  of  Fairbank's  cement  testing  machine.     Show 
the  details  of  the  weighing  mechanism.     Describe  the  test  of  a  tensile 
specimen. 


300  EXPERIMENTAL  ENGINEERING 

CHAPTER  IX. 

100.  In  engine  lubrication  distinguish  between  the  open  system  and 
forced  lubrication.    What  is  the  difference  in  the  character  of  the  oil 
used  in  these  two  systems? 

101.  What  are  the  essential  characteristics  of  the  various  oils  used 
for  lubricating  purposes  at  the  present  time?     Name  and  distinguish 
between  these  various  lubricants. 

102.  What  are  the  principal  determinations  in  making  a  complete  test 
of  a  lubricant?    What  value  have  these  various  tests? 

103.  Make  line  sketch  and  describe  Engler's  or  the  Boverton-Redwood 
viscosimeter. 

104.  Describe  the  method  of  determining  the  following  information  in 
regard  to  a  lubricant:      (1)   flash  point,   (2)    burning  point,   (3)   chill 
point,  (4)  loss  by  evaporation,  (5)  gumming  properties. 

105.  Sketch  and  describe  the  New  York  State  Board  of  Health  or  the 
Cleveland  flash  point  tester. 

106.  Give  a  brief  description  of  an  oil  testing  machine,  illustrating 
with  sketches.    State  the  four  methods  of  observation  in  practice,  for  a 
durability  test. 

107.  Describe  the  preparations  for  and  the  method  of  conducting  an 
oil  durability  test  by  the  Navy  Department  method,  using  an  oil  testing 
machine. 

108.  What  tests  of  oil  can  be  made  on  board  ship?    What  are  the  best 
safeguards  in  purchasing  oil  and  in  using  it? 

CHAPTER  X. 

109.  In  what  ways  may  fuel  economy  be  influenced?    What  qualities 
in  coal  govern  its  selection  as  a  fuel?    What  tests  are  made  on  ship- 
board? 

110.  How  proceed  in  obtaining  a  sample  of  coal  for  test?    Describe  the 
tests  (1)  for  moisture,  (2)  for  volatile  matter,  (3)  for  ash. 

111.  Make  neat  line  sketch  of  Mahler's  fuel  calorimeter.     Letter  and 
name  the  essential  parts. 

112.  Describe  in  detail  the  construction  of  the  bomb  used  with  Mah- 
ler's fuel  calorimeter.    What  are  its  capacity  and  thickness?    Why  is  it 
made  so  large  and  heavy?     State  the  principle  of  operation  of  the 
calorimeter. 

113.  With  the  assistance  of  a   rough  free-hand   sketch  explain   the 
method   of   conducting  a   test   for    calorific   value,   using   the   Mahler 
calorimeter.     What  is  meant  by  the  water  equivalent  and  how  is  its 
value  determined? 

114.  Make  a  neat  sketch  of  Carpenter's  improved  coal  calorimeter 
and  connections.    Letter  and  name  the  essential  parts. 

115.  Draw  a  sectional  view,  showing  the  details  of  the  pressure  re- 
ducer used  in  connection  with  Carpenter's  coal  calorimeter.     Describe 
precautions  in  using. 

116.  With  the  assistance  of  a  free-hand  sketch,  describe  the  method  of 
preparing  for  and  conducting  a  test  for  calorific  value,  using  Carpenter's 
coal  calorimeter. 


QUESTIONS  ON  THE  TEXT  301 

117.  How  is  the  curve  of  calibration  obtained  for  Carpenter's  coal 
calorimeter?    What  is  its  use?     Briefly  state  the  principle  of  the  calo- 
rimeter.    What  is  meant  by  the  corrected  scale  reading  and  how  is  it 
obtained? 

118.  Sketch  Parr's  standard  coal  calorimeter  and  briefly  describe  its 
operation  and  use. 

119.  Sketch   Junker's   calorimeter.     Letter   and   name   the  essential 
parts.     Explain  its  operation  in  determining  the  heating  value  of  a 
gas. 

120.  State  briefly  the  requirements  of  the  navy  specifications  for  fuel 
oil.     What  instruments  are  contained  in  the  navy  portable  test  outfit 
and  what  are  their  uses? 

121.  Sketch  the  Pensky-Marten  apparatus  for  determining  the  flash 
point  and  explain  its  operation. 

122.  What  oils  are  used  on  naval  vessels  as  fuel,  other  than  fuel  oil. 
What  are  the  requirements  for  each? 

CHAPTER  XL 

123.  What  is  the  object  of  making  analyses  of  smoke  pipe  gases? 
Explain  how  the  percentage  of  CO2  is  a  measure  of  the  efficiency  of 
combustion.    What  reagents  are  used  in  flue  gas  analysis?    Explain  the 
use  of  each.    How  obtain  a  sample  of  the  gas? 

124.  Sketch  the  Orsatt-Muencke  apparatus  and  explain  its  operation 
in  flue  gas  analysis.    State  precautions  to  be  observed. 

125.  Having  given  the  results  of  the  chemical  analysis  of  a  fuel  and 
the  results  of  flue  gas  analysis,  burning  this  fuel,  show  how  to  calculate 
the  pounds  of  dry  gas  per  pound  of  combustible. 

126.  Enumerate  the  several  items  that  go  to  make  up  the  heat  balance, 
showing  the  distribution  of  the  heating  value  of  one  pound  of  com- 
bustible, and  explain  briefly  how  each  item  is  calculated. 

127.  Sketch  and   describe  the  Hays   CO2   apparatus  and   explain   its 
operation. 

128.  Make  a   free-hand   sketch   of  the  analyzing  and   recording  ap- 
paratus in  the  Sarco  CO2  recorder,  and  explain  the  operation  of  the 
apparatus. 

129.  Make  diagrammatic  sketch  and  explain  the  essential  principle  of 
the  Uehling  CO2  recorder. 

130.  Explain  the  use  of  time  firing  devices  in  promoting  efficiency  of 
combustion.    Explain  with  line  sketch  the  layout  of  such  an  apparatus 
on  board  ship. 

131.  Draw  diagram  of  one  of  the  following  time  firing  devices  and 
explain  its  operation:     Corey's,  old  type;  Corey's,  new  type;  Kilroy's; 
Sub-Target  Gun  Company's;    General   Electric  Company's,   new  type; 
Lobitz. 


20 


INDEX 


PAGE 

Absolute  temperature    85 

Absorption  dynamometers    161 

Adiabatic  expansion   106 

Air  flow  meter   143 

velocities,   Taylor's  method 130 

Albany   grease    214 

Amsler's  planimeter,  demonstration     33 

description    31 

Anemometer    129 

Averaging  instrument,  Coffin's,  demonstration    37 

description    35 

Bailey  counter   82 

Barrel   calorimeter 101 

Beaume  scale  for  oils 264 

Belt  dynamometers   163 

Bevis-Gibson   flashlight   torsionmeter. 176 

Boiling  point    86 

Boverton-Redwood  viscosimeter    217 

Brake,  electric    162 

Brake  horse   power 144,  161 

Brake,  Prony    161 

water    162 

Breaking  load  188 

Bristol's  recording  gage 46 

Calculating  instrument,  Fuller's    27 

Thacher's    30 

Calibration  of  indicator  springs  146 

shafting    169 

Calorimeter,  barrel   101 

Carpenter's   improved   coal 241 

calibration    248 

operation     246 

pressure  reducer  for 

oxygen    244 

separating  steam   99 

throttling    87 

Junker's,  description     254 

operation    256 

Mahler's  fuel,  description    232 

operation     235 

water  equivalent   238 

Parr's  standard  fuel,  description    248 

operation,  anthracite   or    coke. .   253 

oil  fuels    253 

soft  coal   251 

separating  99 

steam    87 

superheating    92 

Thomas  superheating 92 

throttling    ~. 87 

calibration   method    89 

graphic  solution   89 

limitations    .  92 


304  INDEX 

PAGK 

Calorimetric  pyrometer   65 

Carpenter's  improved  coal  calorimeter,  calibration   248 

description    241 

operation    246 

pressure  reducer  for  oxygen  244 

improved  separating  steam  calorimeter 99 

indicator  and  gage  testing  apparatus 147 

Cement,  constancy  of  volume 208 

fineness    207 

hydraulic    205 

mixed    206 

natural    205 

neat    -. 206 

Portland 205 

Pozzuolana  or  Puzzolan 206 

setting    208 

specific  gravity    207 

tensile  strength    207 

tests    209 

testing    207 

testing  machine 210 

test  piece   209 

time  of  setting 207 

uses  on  board  ship 206 

Chest  pressure  and  horse  power  curves 186 

Cleveland   flash  tester 220 

CO2  apparatus,  Hays    272 

Sarco  automatic  recorder,  application    279 

description    274 

Uehling  recorder    279 

Coal,  sampling 230 

selecting    229 

test  for  ash    232 

moisture    231 

heating  value    232 

volatile  matter   231 

testing  on  board  ship 230 

Coefficient  of  strength  at  elastic  limit 188 

ultimate  strength    188 

Coffin's  averaging  instrument,  demonstration    37 

description    35 

Compression  tests   200 

Computations,  preparations  for 15 

Concrete   206 

reenforced    206 

Cooley's  indicator  testing  apparatus 148 

Corey  time  firing  device,  new  type    283 

old   type    281 

Counter,  Bailey    82 

revolution    72 

Taylor 82 

Cross  bending  tests 200 

Cylinder  oil  213 

Darcy's   Pitot  tube 116 

Davison  speed  regulator 79 

Deviations  from  true  measurement. .                                      11 


INDEX  305 

PAGE 

Denny- Johnson  torsiometer    172 

Diagram,  strain    189 

stress-strain    190 

Differential   counter    73 

Duplex   slide  rule 30 

Dynamometers,  absorption   161 

belt    163 

Kenerson  transmission    164 

transmission    163 

transmission,  Emerson   167 

Economy  of  fuel 229 

Efficiency  of  a  machine 144 

Elasticity    187 

modulus    188 

Elastic  limit    187 

coefficient  of  strength 188 

Electric  brake    162 

horse  power   162 

tachometer,  Hopkins   77 

tachometer,   Hutchison    75 

Elongation,   percentage    188 

Emerson   power    scale 167 

Engineering  calculations    9 

Engine  lubrication,  forced    212 

open    212 

Engler's  viscosimeter   216 

Entropy    85 

diagram    102 

of  steam    105 

steam  and  water 105 

water    103 

Error,  limits  of  in  observations 11 

sources  of  12 

Errors  classified 12 

Expansion  pyrometer  63 

Experimental  Engineering  defined 9 

Extensometer,  Riehl£-Kenerson    197 

Factor  of  safety 189 

Fairbanks  cement  testing  machine 210 

Figures,  significant    13 

rules  for 14 

Flashlight   torsionmeter    176 

Flash  tester,  Cleveland    220 

New  York  State  Board  of  Health 219 

Pensky-Martens    261 

Tagliabue    265 

Flash  test,  open  cup 219 

Flue  gas  analysis    266 

calculations    269 

combustion  losses    271 

Formula  for  air  velocities,  Pitot's  tube 133 

flow  of  steam,  Napier's 133 

Fottinger  torsionmeter   177 

Fuel  economy  229 

Fuller's  calculating  instrument 27 


306  INDEX 

PAGE 

Gage,  hook     124 

tester 52 

testing  apparatus,  Carpenter's    148 

dead   weight    51 

Gages,  Bourdon    44 

compound     45 

recording  pressure    45 

diaphragm    44 

pressure    43 

testing 51 

testing  vacuum  53 

vacuum    43 

Gasoline,  specifications  for 265 

Gas  thermometer  54 

General  Electric  Company,  steam  meter  138 

time  firing  device,  new  type 288 

Hays  COo  apparatus 272 

Heat,  defined    85 

Hook  gage   124 

Hopkins  electric  tachometer 77 

Hopkinson-Thring  torsionmeter   179 

Horse  power    144 

electric    162 

Hospitalier-Carpentier  Manograph   151 

Hudson's  horse  power  scale 158 

Hutchison  marine  tachometer 75 

Hydraulic  cement   205 

Ice  machine  oil 214 

Inch,  Miner's    128 

Indicated  horse  power 144 

Indicator,  errors  of    145 

maneuvering    72 

Ripper's   mean   pressure 153 

springs,    calibration    146 

testing  apparatus,  Carpenter's    147 

Cooley's    148 

torsion    203 

Industrial  Thermograph   57 

Isothermal   expansion    106 

Joule's  equivalent   86 

Junker's  calorimeter,  description    254 

operation    256 

Kenerson  transmission  dynamometer 164 

Keystone  water  meter Ill 

Kilroy  time  firing  device 284 

Latent  heat  86 

Limits  of  error  in  observations 11 

Load,  breaking    188 

maximum     188 

safe    188 

Lobitz  time  firing  device 391 

Logarithmic  scale    17 

horse  power    158 

McNab  marine  register 78 

Mahler's  fuel  calorimeter,  description     232 

operation    235 

water   equivalent    238 


INDEX  307 

PAGE 

Maneuvering  indicator  72 

Manograph,  Hospitalier-Carpentier    151 

Manometers    53 

Manometer  for  measuring  air  velocities 131 

Maximum  load   188 

Mean  pressure  indicator,  Ripper's 153 

Measurements,  true,  deviations  from 11 

direct  and  indirect 11 

Measuring  machines  40 

Mercurial   pyrometer    60 

Meter,  Venturi   112 

Meters,  steam 134 

steam,  series    134 

shunt    138 

water    110 

Metric  horse   power 144 

Metten  torsionmeter  183 

Miner's  inch    128 

Mistakes   13 

Modulus  of  elasticity 188 

Modulus  of  resilience 188 

Napier's  formula  133 

New  York  State  Board  of  Health  Flash  Tester 219 

Observations,  arithmetical  mean    12 

weighted  mean    12 

Oil,  cylinder    213 

Oil  fuel,  Beaume   scale    264 

fire  test  263 

flash   test    261 

navy  specifications    259 

specific  gravity  263 

test  for  water  and  sediment 263 

testing,  navy  portable  outfit 261 

Oil,  ice  machine  214 

kerosene,  specifications  for 264 

lard    264 

lubricating,  for  forced  lubrication 213 

wick  or  gravity  feed 213 

mineral,  specifications  for 264 

Vaclite    264 

test,  acid    222 

burning  point  221 

cold    222 

evaporation    222 

Oil  test,  flash    219 

gumming  or  drying 219 

specific  gravity   215 

viscosity    215 

Oil  testing,  determinations  required  214 

log    227 

machine    •. 222 

methods  with  machine 224 

Navy  Department  method • 225 

on  board  ship 227 

Omnimetre,   Sexton's    18 

Orsatt-Muencke  Apparatus,  description    266 

operation    268 


308  INDEX 

PAGE 

Parr  standard  fuel  calorimeter,  description    248 

operation,  soft  coal 251 

anthracite  or  coke 253 

oil  fuels 253 

Pensky-Martens   flash   tester 261 

Percentage  of  elongation 188 

Phosphor-bronze,  tests  of 201 

Pitot's  tube    144 

for  air  130 

single,  for  air  velocities 133 

Pitometer    119 

rod  meter 119 

street  connection  121 

traverse    121 

U  tube    121 

Planimeters    31 

Planimeter,  Amsler's,  demonstration    33 

description    31 

Coffin's  averaging  instrument,  demonstration   37 

description    35 

Pneumatic  pyrometer,  Uehling's 57 

Portable  tachometer   75 

Power  board,  Ripper's 157 

Power,  defined    144 

Power  scale,  Emerson 167 

Pratt  and  Whitney  measuring  machine 40 

Precision  tacograph   83 

Prony  brake    161 

Pyrometers   54 

Pyrometer,  calorimetric   65 

expansion    63 

mercurial    60 

reflecting    71 

resistance    67 

thermo-electric   66 

Uehling's  pneumatic    67 

Quality  of  steam 87 

Quantity  of  heat 85 

Recorder,  Uehling's  differential  pressure 49 

Recording  pressure  gage 45 

Reduction  of  area 188 

Reflecting  pyrometer   71 

Reports,  how  made 16 

Resilience,  modulus   188 

Resistance  thermometer   67 

Revolution  counters   72 

Revolution  counter,  differential 73 

Riehle-Kenerson   extensometer    197 

RiehlS  screw  power  testing  machine 191 

Rigidity    188 

Ripper's  mean  pressure  indicator 153 

power  board    157 

Rod  meter  for  pitometer 119 

Rules  for  significant  figures 14 

Safe  load   188 

Safety,  factor  189 

Sampling   coal    230 


INDEX  309 

PAGE 

Sarco  automatic  CO2  recorder,  application    279 

description    274 

steam  meter   134 

Saturated   steam    86 

Scale,  logarithmic   17 

Selecting  coal   229 

Sensible  heat    86 

Sexton's  omnimetre    18 

Shaft  horse  power 144 

Shafting,  calibration    169 

Shearing  tests    201 

Significant  figures    13 

rules  for    13 

Slide  rule,  double  scale    28 

duplex    30 

Puller's    27 

horse   power    158 

Sexton's  omnimetre    18 

Sperry's  pocket  calculator 27 

straight    28 

Thacher's    30 

Sources  of  error 12 

Specific  heat   86 

Speed  regulator,  Davison 79 

Sperry's  pocket  calculator 27 

Steam  calorimeters    87 

flow  meter,  indicating    143 

recording    139 

meters    134 

meter,  General   Electric  Co 138 

Sarco    134 

sampling    , 102 

Stiffness    188 

Strain    187 

diagram    189 

Strength  of  materials 187 

Stress    187 

Stress-strain  diagram   190 

Sub-Target  Gun  Co.'s  time  firing  device 286 

Superheated  steam   87 

Tacograph,   precision    83 

Tachometers    73 

Tachometer,  Hopkins  electric  77 

Hutchison   marine   75 

portable    75 

Tagliabue  flash  tester 265 

Tallow    214 

Tank  for  weir  apparatus 125 

Taylor  counter   82 

method  for  low  air  velocities 130 

Temperature    85 

Temperature-entropy  diagram    102 

ideal  engine   106 

real  engine   107 

measurement    53 

Testing  machines    190 


310  INDEX 

PAGE 

Testing  machine,  autographic  apparatus  196 

automatic  apparatus    196 

cement    210 

compression  tests   200 

cross  bending  tests 200 

driving  mechanism   195 

oil    222 

practical  use 197 

Riehl6-Miller,  torsional  202 

Richie"  screw  power 191 

screw  and  vernier  beams 195 

shearing  tests 201 

straining  mechanism  191 

test  record    199 

weighing  apparatus   194 

pressure  gages   51 

vacuum  gages   53 

Test    pieces,    standard 202 

Thacher's  calculating  instrument 30 

Thermal  unit   86 

Thermo-electric  pyrometer   66 

Thermograph,   Industrial    57 

Thermometer,  gas   54 

high  temperature    54 

resistance    67 

Thomas  superheating  calorimeter 92 

Time  firing  devices,  general  description   280 

device,  Corey,  new  type    283 

old  type    281 

General  Electric  Co.,  new  type 288 

Kilroy    284 

Lobitz    291 

Sub-Target   Gun   Co 286 

Torsion   indicator    203 

readings  on  reciprocating  engines 186 

Torsional  testing  machine 202 

Torsionmeters    169 

Torsionmeter  and  indicator  compared 184 

Torsionmeter,  Bevis-Gibson  flashlight    176 

Denny-Johnson    172 

Fottinger 177 

Hopkinson-Thring    179 

horse  power  without  calibration 171 

Metten    183 

Total  heat   86 

Transmission  dynamometers   163 

Uehling  CO2  recorder  279 

differential  pressure  recorder 49 

pneumatic  pyrometer  57 

Ultimate  strength    188 

Vaclite    264 

Vaseline    214 

Venturi   meter    112 

Viscosimeter,  Boverton-Redwood    217 

Engler's    216 


INDEX  311 

PAGE 

Water  brake    162 

meters    110 

meter,  Keystone   Ill 

Worthington     110 

Webb,  C.  A.,  oil  testing,  method 225 

Weirs    122 

Weir,  tank  125 

triangular    126 

Wet  steam   86 

Worthington  water  meter 110 


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